Optical filter apparatus and associated method

ABSTRACT

An apparatus and associated method for altering the propagation constant of a region of filtering propagation constant in an optical waveguide. The method comprising positioning an electrode of an electrode shape proximate the waveguide. An altered region of filtering propagation constant is projected into the waveguide that corresponds, in shape, to the electrode shape by applying a voltage to the shaped electrode. The propagation constant of the region of filtering propagation constant is controlled by varying the voltage. Such filter embodiments as an Infinite Impulse Response filter and a Finite Impulse Response filter may be provided.

FIELD OF THE INVENTION

[0001] This invention relates to optical devices, and more particularlyto optical waveguide devices.

BACKGROUND OF THE INVENTION

[0002] In the integrated circuit industry, there is a continuing effortto increase device speed and increase device densities. Optical systemsare a technology that promise to increase the speed and current densityof the circuits. Optical filters are optical devices that are configuredto perform filtering functions. It is known to provide many filteringfunctions using optical devices. For instance, arrayed waveguidewavelength multiplex an input optical signal into a plurality of outputoptical signals, each of the output optical signals having its distinctbandwidth that was originally contained in the input optical signal. Assuch, the arrayed waveguide may be considered as a wavelength filter.Optical deflectors can be discrete elements made from glass or clearplastic, or alternatively can be formed from a semiconductor material,such as silicon.

[0003] Optical filters, as with most optical devices, are susceptible tochanges in such operating parameters as temperature, device age, devicecharacteristics, contact, pressure, vibration, etc. As such, the opticalfilters are typically contained in packaging that maintains theconditions under which the optical devices are operating. Providing suchpackaging is extremely expensive. Even if such packaging is provided,passive optical filters may be exposed to slight condition changes. Assuch, the passive optical filters perform differently under thedifferent conditions. For example, the filters will filter lightdifferently depending on the conditions. If the characteristics of apassive optical filter is altered outside of very close tolerances, thenthe optical filter will not adequately perform its function. In otherwords, there is no adjustability to the passive optical filters.

[0004] As such it would be desirable to provide an optical filter thatcan adjustably filter light to provide a variety of filteringoperations. Additionally, it would be desirable to provide a mechanismto compensate in optical filters for variations in the operatingconditions.

SUMMARY OF THE INVENTION

[0005] The present invention is directed to an apparatus and associatedmethod for altering the propagation constant of a region of filteringpropagation constant in an optical waveguide. The method comprisingpositioning an electrode of an electrode shape proximate the waveguide.An altered region of filtering propagation constant is projected intothe waveguide that corresponds, in shape, to the electrode shape byapplying a voltage to the shaped electrode. The propagation constant ofthe region of filtering propagation constant is controlled by varyingthe voltage. Such filter embodiments as an Infinite Impulse Responsefilter and a Finite Impulse Response filter may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings, which are incorporated herein andconstitute part of this specification, illustrate the presentlypreferred embodiment of the invention, and, together with the generaldescription given above and the detailed description given below, serveto explain features of the invention.

[0007]FIG. 1 shows a front cross sectional view of one embodiment of anoptical waveguide device including a field effect transistor (FET);

[0008]FIG. 2 shows a top view of the optical waveguide device shown inFIG. 1;

[0009]FIG. 3 shows a section view as taken through sectional lines 3-3of FIG. 2;

[0010]FIG. 4 shows a front cross sectional view of one embodiment of anoptical waveguide device including a metal oxide semiconductor capacitor(MOSCAP);

[0011]FIG. 5 shows a front view of another embodiment of an opticalwaveguide device including a high electron mobility transistor (HEMT);

[0012]FIG. 6 shows a graph plotting surface charge density and the phaseshift, both as a function of the surface potential;

[0013]FIG. 7 shows one embodiment of a method to compensate forvariations in temperature, or other such parameters, in an opticalwaveguide device;

[0014]FIG. 8 shows another embodiment of a method to compensate forvariations in temperature, or other such parameters, in an opticalwaveguide device;

[0015]FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100;

[0016]FIG. 10 shows a side cross sectional view of one embodiment of aridge optical channel waveguide device;

[0017]FIG. 11 shows a side cross sectional view of one embodiment of atrench optical channel waveguide device;

[0018]FIG. 12 shows one embodiment of a wave passing though a dielectricslab waveguide;

[0019]FIG. 13 shows a top view of another embodiment of an opticalwaveguide device from that shown in FIG. 2, including one embodiment ofa prism-shaped gate array that provides for light deflection by theoptical device;

[0020]FIG. 14 shows a top cross sectional view of the waveguide of theembodiment of prism-shaped gate array of FIG. 13 including dotted linesrepresenting a region of changeable propagation constant. The solidlight rays are shown passing through the regions of changeablepropagation constant corresponding to the prism-shaped gate array;

[0021]FIG. 15, including FIGS. 15A to 15D, show side cross section viewsof the optical waveguide device of FIG. 13 or taken through sectionallines 15-15 in FIG. 13, FIG. 15A shows both gate electrodes 1304, 1306being deactivated, FIG. 15B shows the gate electrode 1304 being actuatedas the gate electrode 1306 is deactivated, FIG. 15C shows the gateelectrode 1304 being deactivated as the gate electrode 1306 isactivated, and FIG. 15D shows both gate electrodes 1304 and 1306 beingactuated;

[0022]FIG. 16 shows a top view of another embodiment of an opticalwaveguide device that is similar in structure to the optical waveguidedevice shown in FIG. 2, with a second voltage source applied from thesource electrode to the drain electrode, the gate electrode andelectrical insulator is shown partially broken away to indicate theroute of an optical wave passing through the waveguide that is deflectedfrom its original path along a variety of paths by application ofvoltage between the source electrode and gate electrode;

[0023]FIG. 17 shows another embodiment of an optical deflector;

[0024]FIG. 18 shows a top view of one embodiment of an optical switchthat includes a plurality of the optical deflectors of the embodimentsshown in FIGS. 14, 15, or 16;

[0025]FIG. 19 shows a top view of another embodiment of an opticalswitch device from that shown in FIG. 18, that may include oneembodiment of the optical deflectors shown in FIGS. 14, 15, or 16;

[0026]FIG. 20 shows one embodiment of a Bragg grating formed in one ofthe optical waveguide devices shown in FIGS. 1-3 and 5;

[0027]FIG. 21 shows another embodiment of a Bragg grating formed in oneof the optical waveguide devices shown in FIGS. 1-3 and 5;

[0028]FIG. 22 shows yet another embodiment of a Bragg grating formed inone of the optical waveguide devices shown in FIGS. 1-3 and 5;

[0029]FIG. 23 shows one embodiment of a waveguide having a Bragg gratingof the type shown in FIGS. 20 to 22 showing a light ray passing throughthe optical waveguide device, and the passage of reflected lightrefracting off the Bragg grating;

[0030]FIG. 24 shows an optical waveguide device including a plurality ofBragg gratings of the type shown in FIGS. 20 to 22, where the Bragggratings are arranged in series;

[0031]FIG. 25, which is shown exploded in FIG. 25B, shows a respectivetop view and top exploded view of another embodiment of an opticalwaveguide device including a gate electrode configured that may beconfigured as an Echelle diffraction grating or an Echelle lens grating;

[0032]FIG. 26 shows a top cross sectional view taken within thewaveguide of the optical waveguide device illustrating the diffractionof optical paths as light passes through the actuated Echellediffraction grating shown in FIG. 25, wherein the projected outline ofthe region of changeable propagation constant from the Echellediffraction grating is shown;

[0033]FIG. 27 shows an expanded view of the optical waveguide devicebiased to operate as an Echelle diffraction grating as shown in FIG. 26;

[0034]FIG. 28 shows a top cross sectional view taken through thewaveguide of the optical waveguide device illustrating the focusing ofmultiple optical paths as light passes through the actuated Echelle lensgrating shown in FIG. 25, illustrating the region of changeablepropagation constant resulting from the Echelle lens grating;

[0035]FIG. 29 shows an expanded view of the optical waveguide devicebiased to operate as an Echelle lens grating as shown in FIG. 28;

[0036]FIG. 30 shows a top view of one embodiment of an optical waveguidedevice that includes a Bragg grating, and is configured to act as anoptical lens;

[0037]FIG. 30A shows a top cross sectional view taken through thewaveguide of the optical waveguide device shown in FIG. 30 illustratinglight passing through the waveguide;

[0038]FIG. 31 shows a top view of another embodiment of opticalwaveguide device that includes a filter grating, and is configured toact as an optical lens;

[0039]FIG. 31A shows a top cross sectional view taken through thewaveguide of the optical waveguide device shown in FIG. 31 illustratinglight passing through the waveguide;

[0040]FIG. 32 shows a top view of another embodiment of opticalwaveguide device that includes a Bragg grating, and is configured to actas an optical lens;

[0041]FIG. 32A shows a top cross sectional view taken through thewaveguide of the optical waveguide device shown in FIG. 32;

[0042]FIG. 33 shows a front view of another embodiment of opticalwaveguide device from that shown in FIG. 1;

[0043]FIG. 34 shows a top view of one embodiment of an arrayed waveguide(AWG) including a plurality of optical waveguide devices;

[0044]FIG. 35 shows a schematic timing diagram of one embodiment of afinite-impulse-response (FIR) filter;

[0045]FIG. 36 shows a top view of one embodiment of an FIR filter;

[0046]FIG. 37 shows a schematic timing diagram of one embodiment of aninfinite-impulse-response (IIR) filter;

[0047]FIG. 38 shows a top view of one embodiment of an IIR filter;

[0048]FIG. 39 shows a top view of one embodiment of a dynamic gainequalizer including a plurality of optical waveguide devices;

[0049]FIG. 40 shows a top view of another embodiment of a dynamic gainequalizer including a plurality of optical waveguide devices;

[0050]FIG. 41 shows a top view of one embodiment of a variable opticalattenuator (VOA);

[0051]FIG. 42 shows a top view of one embodiment of optical waveguidedevice 100 including a channel waveguide being configured as aprogrammable delay generator 4200;

[0052]FIG. 43 shows a side cross sectional view of the FIG. 42embodiment of programmable delay generator 4200;

[0053]FIG. 44 shows a top view of one embodiment of an optical resonatorthat includes a plurality of optical waveguide devices that act asoptical mirrors;

[0054]FIG. 45 shows a top cross sectional view taken through thewaveguide of the optical resonator shown in FIG. 44;

[0055]FIG. 46 shows a top view of one embodiment of an optical waveguidedevice configured as a beamsplitter;

[0056]FIG. 47 shows a top view of one embodiment of a self aligningmodulator including a plurality of optical waveguide devices;

[0057]FIG. 48 shows a top view of one embodiment of a polarizingcontroller including one or more programmable delay generators of thetype shown in FIGS. 42 and 43;

[0058]FIG. 49 shows a top view of one embodiment of an interferometerincluding one or more programmable delay generators of the type shown inFIGS. 42 and 43; and

[0059]FIG. 50 shows a flow chart of method performed by the polarizationcontroller shown in FIG. 48.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0060] The present disclosure provides multiple embodiments of opticalwaveguide devices in which light travels within a waveguide. Differentembodiments of optical waveguide devices are described that performdifferent functions to the light contained in the waveguide. Alteringthe shape or structure of an electrode(s) can modify the function of theoptical waveguide device 100.

[0061] There are a variety of optical waveguide devices 100 that aredescribed in this disclosure. Embodiments of optical waveguide devicesinclude a waveguide located in a Field Effect Transistor (FET) structureas shown in FIGS. 1 to 3; a waveguide associated with metal oxidesemiconductor capacitor (MOSCAP) structure is shown in FIG. 4; and awaveguide located in the High Electron Mobility Transistor (HEMT) asshown in FIG. 5. In MOSCAPs, one or more body contact(s) is/areseparated from the gate electrode by a semiconductor waveguide and anelectrical insulator. In the embodiment of FETs applied to the presentinvention, a substantially constant potential conductor is appliedbetween the source electrode and the drain electrode to maintain the twoelectrodes at a common voltage. When the source electrode of a FET isheld at the same potential as the drain electrode, the FET functionallyoperates as, and may be considered structurally to be, a MOSCAP. To makethe description for the above embodiments more uniform, the term “bodycontact electrodes” is used to describe either the body contact at thebase of the MOSCAP or the substantially common potential sourceelectrode and drain electrode in the FET.

[0062] The application of the voltage between the gate and bodycontact(s) predominantly changes the distribution of free-carriers(either electrons or holes) near the semiconductor/electrical insulatorboundary. These essentially surface localized changes in the freecarrier distributions are referred to as two-dimensional electron gas or2DEG included in MOSCAPs. In a FET structure, for example, an increasein the application of the bias leads consecutively to accumulation ofcharges (of the same type as the semiconductor i.e. holes in a p-typeand electrons in n-type, depletion, and finally inversion. In 2DEGs, thepolarity of semiconductor is opposite the type of the predominant freecarriers, i.e. electrons in p-type or holes in n-type). In a HighElectron Mobility Transistor (HEMT), the electron (hole) distributionformed just below the surface of the electrical insulator is referred toas 2DEG because of particularly low scattering rates of charge carriers.At any rate, for the purposes of clarity, all of the above shall bereferred to as 2DEG signifying a surface localized charge density changedue to application of an external bias.

[0063] The term “semiconductor” is used through this disclosure inparticular reference to the waveguides of the particular opticalwaveguide devices. The semiconductor waveguide is intended to representa class of semiconductor materials. Silicon and Germanium are naturalsingle element semiconductors at room temperature. GaAs and Inp areexamples of binary compound semiconductors. There are semiconductorsmade from three element semiconductors such as AlGaAs. The salientfeature of all semiconductors is the existence of a band-gap between thevalence and the conduction band. Multiple layers of semiconductors mayalso be used in the construction of a waveguide as well as to create anoptical waveguide device including a MOSCAP, a FET, or a HEMT. For thepurpose of this disclosure, the semiconductor provides the ability tocontrol the density of the 2DEG by the application of the gate voltage.Any description of a specific semiconductor in this disclosure isintended to be enabling, exemplary, and not limiting in scope. Theconcepts described herein are intended to apply to semiconductors ingeneral.

[0064] These concepts relating to the optical waveguide device applyequally well to any mode of light within a waveguide. Therefore,different modes of light can be modulated using multi-mode waveguides.The physical phenomena remains as described above for multi-modewaveguides.

[0065] I. Optical Waveguide Device

[0066] The embodiments of optical waveguide device 100 shown in multiplefigures including FIGS. 1-3, and 5, etc. include a field effecttransistor (FET) portion 116 that is electrically coupled to a waveguide106. One embodiment of the waveguide is fabricated proximate to, andunderneath, the gate electrode of the FET portion 116. The waveguide istypically made from silicon or another one or plurality of III-Vsemiconductors. The FET portion 116 includes a first body contactelectrode 118, a gate electrode 120, and a second body contact electrode122. A voltage can be applied by e.g., a voltage source 202 to one ofthe electrodes. The gate electrode 120 is the most common electrode inwhich the voltage level is varied to control the optical waveguidedevice.

[0067] The variation in voltage level changes the propagation constantof at least a portion of the waveguide 106. The changes in the indexprofile of the waveguide are determined by the location and shapes ofall the electrodes. The density of the 2DEG generally follows the shapeof the gate electrode 120. Therefore, the shape of the gate electrodemay be considered as being projected into a region of changeablepropagation constant 190 (the value of the propagation constant may varyat different locations on the waveguide 106). The region of changeablepropagation constant 190 is considered to be that region through theheight of the waveguide in which the value of the propagation constantis changed by application of voltage to the gate electrode 120. Gateelectrodes 120 are shaped in non-rectangular shapes (as viewed fromabove or the side depending on the embodiment) in the differentembodiments of optical waveguide device. The different embodiments ofthe optical waveguide device perform such differing optical functions asoptical phase/amplitude modulation, optical filtering, opticaldeflection, optical dispersion, etc. Multiple ones of the opticalwaveguide devices can be integrated into a single integrated opticalcircuitry as an arrayed waveguide (AWG), a dynamic gain equalizer, and alarge variety of integrated optical circuits. Such optical waveguidedevices and integrated optical circuits can be produced using largelyexisting CMOS and other semiconductor technologies.

[0068] FIGS. 1 to 3 will now be described in more detail, andrespectively show a front, top, and side view of one embodiment of anoptical waveguide device 100. FIG. 1 shows a planar semiconductorwaveguide bounded by low-index insulating materials to which the lightis coupled using a prism coupler 112. Other well-known types of couplinginclude gratings, tapers, and butt-coupling that are each coupled to theend of the waveguide. The “gate” electrode 120 is positioned directlyabove the light path in the semiconductor waveguide. The gate electrodeis separated from the semiconductor by the low-index dielectric actingas an electrical insulator. The body contact electrodes are electricallycoupled to the semiconductor. This embodiment may be considered to be aFET structure with the body contact electrodes 118, 122 forming asymmetric structure typically referred to as “source” and “drain” in FETterminology. A substantially constant potential conductor 204 equalizesthe voltage level between the first body contact electrode 118 and thesecond body contact electrode 122. The first body contact electrode andthe second body contact electrode can thus be viewed as providingsymmetrical body contact electrodes to the semiconductor. In anotherembodiment, the body contact is placed directly underneath the lightpath and underneath the waveguide.

[0069] In yet another embodiment, the body contact is positionedsymmetrically laterally of both sides of, and underneath, the incidentlight path within the waveguide. The body contact in each of theseembodiments is designed to change a free-carrier distribution region ina two dimensional electron gas (2DEG) 108 near thesemiconductor/electrical insulator boundary of the waveguide along thelight travel path. This change in free-carrier distribution results fromapplication of the potential between the insulated gate electrode andthe one or plurality of body contact electrodes connected to the body ofthe semiconductor.

[0070] The FIG. 1 embodiment shows the optical waveguide device 100including an integrated field effect transistor (FET) portion 116. Thefield effect transistor (FET) portion 116 includes the gate electrode120, the first body contact electrode 118, and the second body contactelectrode 122, but the channel normally associated with a FET is eitherreplaced by, or considered to be, the waveguide 106. Examples of FETsthat can be used in their modified form as FET portions 116 (by usingthe waveguide instead of the traditional FET channel) include ametal-oxide-semiconductor FET (MOSFET), a metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor FET(MESFET), a modulation doped FET (MODFET), a high electron mobilitytransistor (HEMT), and other similar transistors. In addition, ametal-oxide-silicon capacitor (MOSCAP) may also be similarly modified toform a FET portion.

[0071]FIGS. 1, 2, and 3 shows one embodiment of optical waveguide device100 that includes a substrate 102, a first electrical insulator layer104, a waveguide 106, a first body contact well 107, a second bodycontact well 109, the 2DEG 108, a second electrical insulator layer 110,an input prism 112, an output prism 114, and the field effect transistor(FET) portion 116. The 2DEG 108 is formed at the junction between thesilicon waveguide 106 and the second electrical insulator layer 110 ofthe waveguide 106. Multiple embodiments of optical waveguide devices aredescribed that, upon bias of the gate electrode 120 relative to thecombined first body contact electrode 118 and second body contactelectrode 122, effect the passage of light through the waveguide 106 toperform a variety of functions.

[0072] The FIG. 12 embodiment of semiconductor waveguide (which may bedoped) 106 has a thickness h, and is sandwiched between the firstelectrical insulator layer 104 and the second electrical insulator layer110. The first electrical insulator layer 104 and the second electricalinsulator layer 110 are each typically formed from silicon dioxide(glass) or any other electrical insulator commonly used insemiconductors, for example SiN. The electrical insulator layers 104,110 confine the light using total internal reflection of the lighttraversing the waveguide 106.

[0073] Light is injected into the waveguide 106 via the input prism 112and light exits from the waveguide 106 via the output prism 114,although any light-coupling device can be used to respectively inject orremove the light from the waveguide 106. Examples of light-couplingdevices include prisms, gratings, tapers, and butt-couplings. Lightpassing from the input prism (or other input port) to the output prism(or other output port) follows optical path 101 as shown in FIG. 1. Theoptical path 101 may be defined based upon the function of the opticalwaveguide device 100. For example, if the optical waveguide devicefunctions as an optical modulator, optical deflector, or an opticalfilter, the optical path 101 can be respectively considered to be anoptical modulation region, an optical deflection region, or an opticalfiltering region, etc.

[0074] As described earlier, application of voltage on the gateelectrode 120 relative to the combined first body contact electrode 118and second body contact electrode 122 leads to a change in thepropagation constant via changes induced in the free-carrier densitydistribution 108. In a MOSCAP, the capacitance of the device iscontrolled by the voltage due to presence (or absence) of 2DEG. In caseof a FET, changes in the free carrier distribution also control theconductance between the first body contact electrode and the second bodycontact electrode. The free-carriers are responsible for changing theoptical phase or the amplitude of the guided wave depending on theirdensity which in turn is controlled by the gate voltage. The basis offield-effect transistor action, i.e., rapid change in 2DEG as a functionof gate voltage, is also responsible for the control of the light waveand enables integration of electronic and optical functions on the samesubstrate. Thus traditional FET electronic concepts can be applied toprovide active optical functionality in the optical waveguide device100. The FET portion 116 is physically located above, and affixed to,the waveguide 106 using such semiconductor manufacturing techniques asepitaxial growth, chemical vapor deposition, physical vapor deposition,etc.

[0075] The propagation constant (and therefore the effective mode index)of at least a portion of the waveguide in the optical waveguide device100 is changed as the free carrier distribution 108 changes. Suchchanging of the propagation constant results in phase modulation of thelight passing through that device. The phase modulation occurs in aregions of changeable propagation constant, indicated in cross-hatchingin FIGS. 1 and 3 as 190, that closely follows the two-dimensional planarshape of the gate electrode through the height of the waveguide to forma three dimensional shape.

[0076]FIG. 2 shows one embodiment of a voltage source configuration thatbiases the voltage of the optical waveguide device 100 by using avoltage source 202 and a substantially constant potential conductor 204.The substantially constant potential conductor 204 acts to tie thevoltage level of the first body contact electrode 118 to the voltagelevel of the second body contact electrode 122. The voltage source 202biases the voltage level of the gate electrode 120 relative to thecombined voltage level of the first body contact electrode 118 and thesecond body contact electrode 122.

[0077] To apply a voltage to the gate electrode, a voltage source 202applies an AC voltage V_(g) from the gate electrode 120 to the combinedfirst body contact electrode 118 and second body contact electrode 122.The AC voltage V_(g) may be configured either as a substantially regular(e.g. sinusoidal) signal or as an irregular signal such as a digitaldata transmission. In one embodiment, the AC voltage V_(g) may beconsidered as the information carrying portion of the signal. Thevoltage source 202 can also apply a DC bias V_(g) to the gate electrode120 relative to the combined first body contact electrode 118 and secondbody contact electrode 122. Depending on the instantaneous value of theV_(g), the concentration of the 2DEG will accumulate, deplete, or invertas shown by the different regions in FIG. 6. In one embodiment, the DCbias V_(g) is the signal that compensates for changes in deviceparameters. The combined DC bias V_(g) and AC voltage v_(g) equals thetotal voltage V_(G) applied to the gate electrode by the voltage source202. It will be understood from the description above that modulation ofv_(g) can thus be used to effect, for example, a correspondingmodulation of light passing through the waveguide 106.

[0078] The voltage potential of the first body contact electrode 118 istied to the voltage potential of the second body contact electrode 122by the substantially constant potential conductor 204. Certainembodiments of the substantially constant potential conductor 204include a meter 205 (e.g. a micrometer) to measure the electricalresistance of the gate electrode from the first body contact electrodeto the second body contact electrode. The term “substantially” is usedwhen referring to the constant potential conductor because the meter 205may generate some relatively minor current levels in comparison to theoperating voltage and current levels applied to the optical waveguidedevice. The minor current levels are used to measure the resistance ofthe gate electrode. The current level produced by the meter isrelatively small since the voltage (typically in the microvolt range) ofthe meter is small, and the waveguide resistance is considerable(typically in the tens of ohms).

[0079] The electrical resistance of the gate electrode is a function ofsuch parameters as gate voltage, temperature, pressure, device age, anddevice characteristics. As such, the voltage (e.g. the AC voltage or theDC voltage) applied to the gate electrode can be varied to adjust theelectrical resistance of the gate electrode to compensate for suchparameters as temperature, pressure, device age, and/or devicecharacteristics. Therefore, the voltage applied to the gate electrodecan be adjusted to compensate for variations in the operating parametersof the optical waveguide device.

[0080] As the temperature of the optical waveguide device varies, the DCbias V_(g) applied to the gate electrode 120 of the optical waveguidedevice is adjusted to compensate for the changed temperature. Otherparameters (pressure, device age, device characteristics, etc.) can becompensated for in a similar manner as described for temperature (e.g.using a pressure sensor to sense variations in pressure). Thisdisclosure is not limited to discussing the sensing and compensating fortemperature since the other parameters can be compensated for in asimilar manner. Different meter 205 and/or controller 201 embodimentsmay be provided to compensate for the different temperatures.

[0081]FIG. 7 shows an embodiment of method 700 that compensates fortemperature variations in an optical waveguide device. The method 700starts with step 702 in which the temperature sensor 240 determines thetemperature of the optical waveguide device. The temperature sensor 240can be located either on the substrate or off the substrate. Thetemperature sensor inputs the temperature determined by the temperaturesensor to the controller 201 in step 703. The method 700 continues tostep 704 in which the DC bias V_(g) that is applied to the gateelectrode is adjusted to compensate for variations in the temperature.The controller 201 includes stored information that indicates therequired change in DC bias ΔV_(g) that is necessary to compensate forvariations in temperature, for each value of DC bias V_(g) for eachtemperature within the operating range of the optical waveguide device.The method 700 continues to step 706 in which the AC voltage v_(g) isapplied to operate the optical waveguide device as desired in thewaveguide.

[0082] The amount of AC voltage v_(g) is then superimposed on the DCbias V_(g) that is applied to the gate electrode to provide for thedesired operation of the optical waveguide device 200 (e.g. the voltagenecessary for optical modulation, optical filtering, optical focusing,etc.). The AC voltage v_(g) superimposed on the combined DC bias V_(g)and the DC bias change ΔDC yields the total signal V_(G) applied to thegate electrode.

[0083] Another embodiment of compensation circuit, that compensates forthe change in temperature or other operating parameter(s) of the opticalwaveguide device, measures the electrical resistance of the gate betweenthe first body contact electrode 118 and the second body contact 122.The electrical resistance of the waveguide is a function of temperature,device age, device characteristics, and other such parameters. The meter205 measures the electrical resistance of the waveguide. For a givenwaveguide, the same resistance corresponds to the same electron densityand the same hole density in the waveguide. Therefore, if the sameelectrical resistance of the waveguide is maintained, the opticalwaveguide will behave similarly to cause a similar amount of suchoptical action as optical modulation, optical filtering, opticalfocusing, or optical deflection.

[0084]FIG. 8 shows another method 800 used by the controller 201 tocompensate for temperature variations of the optical waveguide device.The method 800 starts with step 802 in which the meter 205 measures theelectrical resistance of the waveguide. The method 800 continues to step804 in which the measured electrical resistance of the waveguide istransferred to the controller 201. The method continues to step 806 inwhich the controller applies the amount of DC bias V_(g) required to beapplied to the gate electrode for that particular value of electricalresistance of the waveguide. Such parameters as temperature and deviceage that together may change the electric resistance of the waveguidecan thus be compensated for together. Therefore, after measuring theelectrical resistance of the waveguide, a feedback loop applies thevoltage for that measured resistance. The method 800 continues to step808 in which the AC voltage v_(g) is applied to operate the opticalwaveguide device (i.e. modulate, filter, focus, and/or deflect light) asdesired in the waveguide.

[0085] In both of these temperature compensating embodiments shown inFIGS. 7 and 8, the controller 201 allows the DC bias V_(g) to driftslowly as the temperature varies to maintain the average resistance ofthe waveguide from the source electrode to the drain electrodesubstantially constant. These temperature-compensating embodiments makethe optical waveguide device exceedingly stable. As such, the requiredcomplexity and the associated expense to maintain the temperature andother parameters over a wide range of temperature are reducedconsiderably.

[0086] Suitably changing the voltages applied between the gate electrode120, and the combined first body contact electrode 118 and second bodycontact electrode 122 results in a corresponding change in the freecarrier distribution in the 2DEG 108. In the FIG. 1 embodiment ofoptical waveguide device 100, altering the voltage applied to the gateelectrode 120 of the FET portion 116 changes the density of freecarriers in the 2DEG 108. Changing free carriers distribution in the2DEG 108 changes the effective mode index of the 2DEG 108 in thewaveguide. Changing the free carrier distribution similarly changes theinstantaneous propagation constant level of the region of changeablepropagation constant 190 (e.g., the area generally underneath the gateelectrode 120 in the FIG. 1 embodiment) within the waveguide 106.

[0087] Effective mode index, and equivalently propagation constant, bothmeasure the rate of travel of light at a particular location within thewaveguide taken in the direction parallel to the waveguide. For a lightbeam traveling over some distance in some medium at a velocity V, thevelocity V divided by the speed of light in vacuum is the index for thatmedium. Glass has a propagation constant of 1.5, which means lighttravels 1.5 times slower in glass then it does in a vacuum. For thesilicon in the waveguide the propagation constant is about 3.5. Since aportion of the light path travels in silicon and part of the light pathis in the glass, the propagation constant is some value between 1.5 and3.5. Therefore, the light is travelling at some effective speed measuredin a direction parallel to the axial direction of the waveguide. Thatnumber, or speed, is called effective index of the waveguide. Each modeof light has a distinct effective index (referred to as the effectivemode index) since different modes of the waveguide will effectivelytravel at different speeds.

[0088] The effective mode index is the same thing as the propagationconstant for any specific mode of light. The term effective mode indexindicates that the different modes of light within a waveguide travel atdifferent velocities. Therefore there are a plurality of effectiveindexes for a multi-mode waveguide, each effective index corresponds toa different mode of light. The propagation constant (or the effectiveindex) measures the average velocity for a phase of light for specificmode travel parallel to the axis of the waveguide as shown in FIG. 12.The propagation constant multiplied by the length would indicate howlong it takes to go that length. Through this disclosure, the effectiveindex for a mode (the effective mode index) is considered to be the samemeasure as the propagation constant for that mode of light. The termpropagation constant is primarily used throughout the remainder of thedisclosure for uniformity.

[0089] Changing the propagation constant of the waveguide 106 by varyingthe 2DEG 108 can phase modulate or amplitude modulate the light in thewaveguide. Within the waveguide, the degree of modulation is local inthat it depends on the density of 2DEG at a particular location. Theshape of the electrode, or other arrangements of body contactelectrodes, can impose a spatially varying phase or amplitude pattern tothe light beam in the waveguide. This in turn can be used to accomplisha wide variety of optical functions such as variable attenuators,optical programmable filters, switches, etc. on the optical signalsflowing through the waveguide 106.

[0090] A controller 201 controls the level of the total voltage V_(G)applied to the voltage source 202. The optical waveguide device 100 canbe employed in a system that is controlled by the controller 201, thatis preferably processor-based. The controller 201 includes aprogrammable central processing unit (CPU) 230 that is operable with amemory 232, an input/output (I/O) device 234, and such well-knownsupport circuits 236 as power supplies, clocks, caches, displays, andthe like. The I/O device receives, for example, electrical signalscorresponding to a desired modulation to be imposed on light passingthrough the waveguide 106. The controller 201 is capable of receivinginput from hardware in the form of temperature sensors and/or meters formonitoring parameters such as temperature, optical wavelength, lightintensity, device characteristics, pressure, and the like. All of theabove elements are coupled to a control system bus to provide forcommunication between the other elements in the controller 201 and otherexternal elements.

[0091] The memory 232 contains instructions that the CPU 230 executes tofacilitate the monitor and control of the optical waveguide device 100.The instructions in the memory 232 are in the form of program code. Theprogram code may conform to any one of a number of different programminglanguages. For example, the program code can be written in C, C++,BASIC, Pascal, or a number of other languages. Additionally, thecontroller 201 can be fashioned as an application-specific integratedcircuit (ASIC) to provide for quicker controller speed. The controller201 can be attached to the same substrate as the optical waveguidedevice 100.

[0092] In the FIG. 1 embodiment of waveguide 106, electrons (hole)concentrate in the waveguide to form the 2DEG 108 that forms a verynarrow channel near the boundary of the silicon waveguide 106 and thesecond electrical insulator layer 110. The surface inversion chargedensity q_(n) in the 2DEG 108 is a direct function of the local surfacepotential φ_(s) applied to the waveguide 106. The local surfacepotential φ_(s) is, in turn, directly related to the total instantaneousvoltage on the gate electrode 120. The total voltage of light in thewaveguide V_(G) satisfies the equation V_(G)=v_(g)+V_(g), where V_(g) isthe DC bias and v_(g) is the AC bias. The local surface potential φ_(s)is a function of the total voltage V_(G), and is given by the equations:$\begin{matrix}{{\varphi_{s} = {\frac{Q}{C} + V_{G} + \frac{Q_{O\quad X}}{C_{O\quad X}} + \varphi_{m\quad s}}}{\varphi_{s} \equiv {\frac{Q}{C} + V_{G}^{\prime}}}} & 1\end{matrix}$

[0093] The total potential V_(G) that is applied to the waveguide 106 isthus a factor of the effective capacitance C of the optical waveguidedevice 100. The effective capacitance C itself depends on thedistribution of the free-carriers. Thus, the capacitance in the MOS likedevice is a function of the applied voltage. The charges Q andcapacitance C in the equation 1 above are measured per unit area. Sincethe 2DEG density depends only on φ_(s), dopant density, and temperature;2DEG density q_(n) can be plotted vs. φ_(s). FIG. 6 illustrates a curve602 that plots surface charge density as a function of surface potentialfor an Si/SiO₂ MOSCAP where the uniform dopant density is assumed to be10¹⁶ cm⁻² at room temperature. FIG. 6 also shows curve 604 that plotsphase shift that is applied to the optical wave passing throughwaveguide 106 for a 3 mm long rectangular gate region. The phase shiftis plotted as a function of surface potential φ_(s).

[0094] A side view of one embodiment of the optical waveguide deviceincluding a waveguide located in a MOSCAP is shown in FIG. 4. Theoptical waveguide device includes a MOSCAP 400 including a body contact402, a waveguide 106, an electric insulator layer 405, and a gateelectrode 406. In the embodiment of MOSCAP similar to as shown in FIG.4, a voltage source 410 applies a voltage between the gate electrode 406and the body contact 402 to alter a level of propagation constant in aregion of changeable propagation constant 190 within the waveguide 106.The variations to the effective mode index and the propagation constantresult occur similarly to in the FET embodiments of optical waveguidedevice 100 as described below.

[0095] In the MOSCAP embodiment of optical waveguide device shown inFIG. 4, the body contact 402 is positioned below the waveguide 106.Alternatively, body contacts may be located where the traditional sourceand drain electrodes exist on traditional FETs. The body contact in theFET embodiment of optical waveguide device shown in FIGS. 1 to 3 isformed from the first body contact electrode being electrically coupledat the same potential as the second body contact electrode. Applicationof the electric field due to the potential difference between the “gate”and the body contacts results in changes in the distribution of freecharges as shown in the embodiment of FIG. 4.

[0096]FIG. 5 discloses one embodiment of high electron mobilitytransistor (HEMT) 500. The HEMT 500 comprises a semi-electric insulatingsubstrate 502, an undoped buffer waveguide layer 106, an undoped spacerlayer 506, a doped donor layer 508, a 2DEG 505, the first body contactelectrode 118, the gate electrode 120, and the second body contactelectrode 122. In one embodiment, the semi-insulating substrate 502 isformed from AlGaAs. The undoped buffer waveguide layer 106 is formedfrom GaAs. The undoped spacer layer 506 is formed from AlGaAs. The dopeddonor layer 508 is formed from a doped AlGaAs.

[0097] During operation of the optical waveguide device, the 2DEG 505increases in height (taken vertically in FIG. 5) to approximately 20angstroms. The 2DEG 505 is generated at the interface between theundoped spacer layer 506 and the undoped buffer waveguide layer 106 as aresult of the negative biasing of the doped donor layer 508. Suchnegative biasing drives the electron carriers in a 2DEG 505 generallydownward, thereby forming a p-type 2DEG 505. Application of voltage tothe gate electrode tends to increase the free carrier distribution inthose portions of the 2DEG 505 that are proximate the gate electrode.Such an increase in the free carrier distribution in the 2DEG increasesthe effective mode index in the waveguide 106 formed underneath the 2DEG505. The gate electrode 120 is formed having a prescribed electrodeshape. The shape of the effective mode index region within the waveguide106 (i.e., the region having an effective mode index that is changed bythe application of voltage to the gate electrode) generally mirrors theshape of the gate electrode 120 as viewed from above in FIG. 5.Additionally, the undoped spacer layer 506 acts as an insulative layer,to allow the formation of the 2DEG. HEMTs are formed in a variety ofembodiments, several of which are described in U.S. Pat. No. 6,177,685to Teraguchi et al. that issued on Jan. 23, 2001 (incorporated herein byreference in its entirety).

[0098] From semiconductor physics, the change in the distribution offree charges is most pronounced near the electricalinsulator-semiconductor boundary. These changes in the free-carrierdistribution change the index profile of the optical waveguide from awell-known relationship in plasma physics given by the Drude Model. Thechange in the free carrier distribution changes the propagation constantof the optical waveguide device from a well-known relationship in plasmaphysics given by the Drude model in a region of changeable propagationconstant 190 within the waveguide. The changes in the free-carrierdistribution induced in the semiconductor by the application of electricfields between the gate electrode and the body contact electrode(s)modulates the phase and/or amplitude of the optical wave passing throughthe region of changeable propagation constant 190. Thus, local changesin the free carrier distribution induced by a change in applied voltageto the gate electrode are impressed on the local optical phase or theamplitude of light passing through the waveguide. The shape of thecharge distribution, i.e., the region of changeable propagation constant190, provides the appropriate optical function as described below. Inmultiple embodiments, the pattern of the gate electrode (i.e., theplanar shape of the gate) controls the shape of the free carrierdistribution. The change in free carrier distribution, in turn, changesthe local effective mode index, or propagation constant, of thewaveguide in the region of changeable propagation constant 190. The samephenomena of change in the refractive index profile of the waveguide maybe ascribed by indicating that group delay or the group velocity of thelight beam has been changed as the free carrier distribution varies.

[0099] Therefore, the effective mode index, the propagation constant,the group delay, or the group velocity relate to an equivalent concept,namely, parametizing changes in the waveguide's refractive index profileon the optical beam passing through the region of changeable propagationconstant 190 in the waveguide. This principle applies to all embodimentsof optical waveguide devices, including those shown in FIGS. 1-3, 4, and5.

[0100] The relationship between the effective mode index, thepropagation constant, the group delay, or the group velocity apply towaveguides of all thickness' is now considered. In the case of “thick”waveguides, the light ray travels by bouncing between the two boundingplanes defined by the insulator layers 110 and 104. The light ray can beeasily identified, typically using the concept of phase or amplitudechanges that are directly imposed on a beam that has directly undergoneone or multiple interactions with free carriers. However, the conceptsof effective mode index, propagation constant, group delay, or groupvelocity signify the same final result on the light beam. In thisdisclosure, the terms propagation constant, effective mode index, groupdelay, and group velocity are each used to describe the effects ofchanges in the free-carrier distribution due to electric field appliedto a semiconductor in an optical waveguide device, whether the opticalwaveguide device uses FET, HEMT, MOSCAP, or any other type of opticalwaveguide device technology.

[0101] Controlling the 2DEG density provides the optical function of anoptical waveguide device. As described, adjusting the gate voltage cancontrol the 2DEG density. The density may be spatially varied to providemore complex functions. A triangular shaped density distribution(included in a region of changeable propagation constant) is capable ofdeflecting the light beam in a fashion similar to a prism in ordinaryoptics. An undulating pattern of 2DEG of a particular spatial period canreflect/deflect a specific wavelength to form a Bragg grating. The exactshape or the spatial density of the 2DEG is affected by placement ofbody contact electrodes relative to the gate electrode, the shape of thebody contact electrodes and the gate electrode, and the applied voltagesdiscussed herein. The electric field density between the gate electrodeand the body contact electrode determines the shape of the 2DEG density.The properties or thickness of the insulator can be changed to affectthe density distribution. For example, a Bragg grating may beconstructed by patterning the gate electrode as a series of grooveshaving a constant spacing. In alternate embodiments, the gate electrodecan have a consistent thickness, but the insulator thickness or shapecan be altered to change the electrical resistance between the gateelectrode and the waveguide. All of these embodiments provide anelectrically switchable Bragg grating by controlling the 2DEG density.The 2DEG density pattern follows the surface potential at thewaveguide/electric insulator boundary rather than the exact shape of thegate electrode.

[0102]FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100 that is similar to that shown in the embodiment of FIG. 2,except that the optical waveguide device includes an additional bankgate electrode 902 that is connected to a bank gate electrode well 904.The doping charge of the bank gate electrode well 904 (p++) in oneembodiment is opposite the doping charge (n++) of the source electrodewell and the drain electrode well. During operation, a voltage may beapplied between the bank gate electrode 902 and the connected sourceelectrode and drain electrode to establish a propagation constantgradient formed within the region of changeable propagation constantacross the waveguide from the source electrode to the drain electrode. Avariety of alternative embodiments may be provided to establish apropagation constant gradient formed within the region of changedpropagation constant across the waveguide. For example the width of thesecond electrical insulator layer 110, or the resistance of the materialused in the second electrical insulator layer 110 may be varied toestablish a propagation constant gradient across the waveguide. Sincethere are such a variety of FET, MOSCAP, HEMT, and other configurations,it is envisioned that those configurations are within the intended scopeof optical waveguide device of the present invention.

[0103] Optical waveguide devices may be configured either as slabwaveguides or channel waveguides. In channel waveguides, the guidedlight is bound in two directions (x and y) and is free to propagate inthe axial direction. In slab waveguides, the guided light is bound inone direction and can propagate freely in two orthogonal directions.Channel waveguides are used in such applications as transmission,resonators, modulators, lasers, and certain filters or gratings wherethe guided light is bound in two directions. Slab waveguides are used insuch applications as deflectors, couplers, demultiplexers, and suchfilters or gratings where the guided light is bound only in onedirection, and it may be desired to change the direction of propagation.

[0104] There are several embodiments of channel waveguides including theFIG. 10 embodiment of the ridge channel waveguides 1000 and the FIG. 11embodiment trench channel waveguide 1100. The ridge channel waveguide1000 includes a raised central substrate portion 1002, a electricalinsulator layer 1004, and a metal gate electrode 1005. The raisedsubstrate portion 1002 is n-doped more heavily than the main substrate102. The raised substrate portion 1002 forms a channel defined by a pairof side walls 1006, 1008 on the sides; the electrical insulator layer1004 on the top, and the n-doping differential between the raisedsubstrate portion 1002 and the main substrate 102 on the bottom. Thepair of side walls 1006, 1008 includes, or is coated with, a materialhaving a similar index of refraction as the electrical insulator layers104, 106. Biasing the metal gate electrode 1005 forms a 2DEG 108adjacent the electrical insulator layer 1004. The 2DEG 108 allows thecarriers to pass between the first body contact well 107 and the secondbody contact well 109 as applied, respectively, by the respective firstbody contact electrode 118 and the second body contact electrode 122.

[0105]FIG. 11 shows one embodiment of trench channel waveguide 1100. Thetrench channel waveguide includes a plurality of electrical insulativeblocks 1102, 1104 and the waveguide 106. The electrical insulative block1102 partially extends into the waveguide 106 (from the upper surface ofthe optical waveguide device 100) at a lateral location between thefirst body contact well 107 and the gate electrode 120. The electricalinsulative block 1104 partially extends into the waveguide 106 (from theupper surface of the optical waveguide device 100) at a lateral locationbetween the second body contact well 109 and the gate electrode 120. Thelight passing through the waveguide 106 is restrained from travellinglaterally by the addition of the electrical insulative blocks 1102,1104. Spaces 1112, 1114 are defined within the waveguide between eachone of the respective insulative blocks 1102, 1104 and the firstelectrical insulator layer 104. These spaces allow carriers to flowbetween the respective first body contact well 107 and the second bodycontact well 109 through the waveguide 106 formed under the gateelectrode 120.

[0106] One embodiment of the optical waveguide devices 100 can beconstructed on so-called silicon on insulator (SOI) technology that isused in the semiconductor electronics field. SOI technology is based onthe understanding that the vast majority of electronic transistor actionin SO transistors occurs on the top few microns of the silicon. Thesilicon below the top few microns, in principal, could be formed fromsome electrical insulator such as glass. The SOI technology is based onproviding a perfect silicon wafer formed on a layer of an electricalinsulator such as glass (silicon dioxide), that starts two to fivemicrons below the upper surface of the silicon. The electrical insulatorelectrically isolates the upper two to five microns of silicon from therest of the silicon.

[0107] The inclusion of the electrical insulator in SOI electronicdevices limit the large number of electric paths that can be createdthrough a thicker silicon, thereby automatically making SOI transistorsgo faster and use less power consumption. SOI technology has developedover the past decade to be commercially competitive. For example, PowerPC (a registered trademark of Apple Computer, Inc. of Cupertino, Calif.)has moved to SOI technology. In addition, the Pentium lines of processor(Pentium is a registered trademark of Intel Corporation of Santa Clara,Calif.) is soon going to utilize the SOI technology.

[0108] The embodiment of optical waveguide device 100 shown, forexample, in FIGS. 1 to 3 may be configured using SOI technology such asprocessors and chips. The waveguide 106 of the optical waveguide device100 may be fashioned as the upper SOI silicon layer. The firstelectrical insulator layer 104 may be fashioned as the SOI insulatorlayer. The substrate 102 may be fashioned as the SOI silicon substrate.As such, the SOI technology including the majority of processors andchips, can easily be used as an optical waveguide device.

[0109] II. Waveguide Physics

[0110] This section demonstrates that the propagation constant (orequivalently the effective mode index) of the waveguide is aninstantaneous function of the 2DEG charge density q_(n). An increase inthe free carrier distribution in a region of the 2DEG 108 results in acorresponding increase in the propagation constant of the waveguide 106at the corresponding region. The relationship between the volumetricdensity of the free carriers and the refractive index was originallyderived by Drude in his Model of Metals that indicates that metalsprovide both a dielectric and “free electron” response. The same modelmay be applied to semiconductors. The changes in the real part of therefractive index Δn and the imaginary part of the refractive index Δk(the imaginary part corresponds to absorption) from an increase in thefree carrier distribution are a function of the change in thefree-carrier density ΔN, as indicated by the following equations:$\begin{matrix}{{{\Delta \quad n} = {{\frac{e^{2}}{2ɛ_{0}m_{e}n\quad \omega^{2}}\Delta \quad N} \equiv {{\chi\Delta}\quad N}}}{{\Delta \quad k} = \frac{\Delta \quad n}{{\omega\tau}_{s}}}} & 3\end{matrix}$

[0111] where e is the electronic charge, m_(e) is the effective mass ofthe carrier, τ_(s) is the mean scattering time and is related to themobility, and ΔN is the change in the free-carrier density. For thesemiconductor devices considered here, where the dominant change in thefree-carriers is due to the 2DEG, ΔN is a function of q_(n) and thethickness (t) of the 2DEG varies according to the equation:$\begin{matrix}{{\Delta \quad N} = \frac{\Delta \quad q_{n}}{t_{2D\quad E\quad G}}} & 4\end{matrix}$

[0112] TABLE 1 shows the calculated values of the Drude coefficient χand the effective mass m_(e) for Silicon with n or p-type dopants, andGallium Arsinide (GaAs) with n-type doping (at wavelengths of 1.3 and1.55 micron). GaAs and InP both have a larger Drude Coefficient χ thansilicon. This is in part due to the smaller effective mass of charge(electron or hole). Thus, a waveguide structure made from GaAs and InPwill have larger changes in the propagation constant for the samechanges in the density of 2DEG when compared to Silicon. TABLE 1Wavelength Material x m_(e) 1.33 Silicon-n   −7 × 10⁻²² 0.33 1.55 −9.4 ×10⁻²² 1.33 Silicon-p   −4 × 10⁻²² 0.56 1.55 −5.5 × 10⁻²² 1.33 GaAs-n−3.5 × 10⁻²¹ 0.068 1.55 −4.8 × 10⁻²¹

[0113] To estimate the length requirements for a dielectric slabwaveguide, the modes of the FIG. 12 embodiment of dielectric slabwaveguide 106 formed between the cladding layers have to satisfy theequation:

2k _(y) h+φ ₁+φ₂=2mπ  5

[0114] where h is the thickness of the waveguide 106, and the phaseshifts φ₁ and φ₂ are due to the reflection of the light at the boundaryand m is an integer multiple. The propagation constant k_(z) and k_(y)are related to k and the mode angle θ by the following equations:$\begin{matrix}{{k_{y} = {k\quad \cos \quad \theta}}{{k_{z} = {k\quad \sin \quad \theta}},{a\quad n\quad d}}{k = {\left( \frac{2\pi}{\lambda} \right)n}}} & 6\end{matrix}$

[0115] Solving equations 5 and 6 can derive the modes of the waveguide106. The values of φ₁ and φ₂ are functions of angle θ. The change in thepropagation constant k_(z) due to change in the waveguide index profileinduced by the 2DEG is responsible for amplitude and phase modulation.The phase modulation of the light in the waveguide results from a changein the propagation constant of selected regions within the waveguide.The amplitude modulation of the light passing through the waveguideresults from a change in the absorption of the light passing throughselected regions within the waveguide.

[0116] The shape and type of the material through which light is passingplays an important role in determining the optical function of theoptical waveguide device. For example, light passing through rectangularslab optical waveguide device only travels axially along the opticalpath 101. Optical deflectors, for example, not only allow the light totravel axially, but can also deviate the light laterally. The amount ofdisplacement and deviation of the light passing through the waveguideare both dependent on the propagation constant of the waveguide as wellas the apex angle of the prism.

[0117] The shape of a region of changeable propagation constant 190within a waveguide plays a role in determining how an application ofvoltage to the gate electrode will modify the optical characteristics oflight passing through the waveguide. For example, a suitably-biasedprism-shaped gate electrode projects a three dimensional prism-shapedregion of changeable propagation constant 190 into the waveguide. Thecross-sectional height of the region of changeable propagation constant190 is projected through the entire height of the waveguide. As viewedfrom above, the region of changeable propagation constant 190 deflectslight in similar propagation directions as light passing through asimilarly shaped optical prism. In slab waveguides, the rays of lightwill deflect or bounce between the upper and lower surface of thewaveguide while continuing in the same propagation direction as viewedfrom above.

[0118] Unlike actual optical devices that are physically inserted in apath of light, any effects on light passing through the waveguide of thepresent invention due to the propagation constant within a region ofchangeable propagation constant 190 can be adjusted or eliminated byaltering the voltage level applied to the gate electrode. For example,reducing the voltage applied to a deflector-shaped gate electrodesufficiently results in the propagation constant of the projecteddeflector-shaped region of changeable propagation constant 190 beingreduced to the propagation constant value of the volume surrounding theregion of changeable propagation constant 190. In effect, the region ofchangeable propagation constant 190 will be removed. Light travellingthrough the region of changeable propagation constant 190 will thereforenot be effected by the region of changeable propagation constant 190within the waveguide. Similarly, the strength of the propagationconstant can be changed or reversed by varying the voltage applied tothe gate electrode.

[0119] III. Specific Embodiments of Optical Waveguide Devices

[0120] A variety of embodiments of optical waveguide devices are nowdescribed. Each optical waveguide device shares the basic structure andoperation of the embodiments of optical waveguide device describedrelative to FIGS. 1-3, 4, or 5. The optical waveguide device can beconfigured in either the channel waveguide or slab waveguideconfiguration. Each embodiment of optical waveguide device is an activedevice, and therefore, the voltage level applied to the electrode cancontrol the degree that the light within the region of changeablepropagation constant 190 in the waveguide will be affected. Since theoptical waveguide device is active, the propagation constant in theregion of changeable propagation constant 190 can be adjusted by varyingthe voltage applied to the gate electrode. Allowing for such adjustmentusing the controller 201 in combination with either the meter 205 or thetemperature sensor 240 using the methods shown in FIGS. 7 or 8 is highlydesirable considering the variation effects that temperature, deviceage, pressure, etc. have on the optical characteristics of the opticalwaveguide device.

[0121] The embodiments of optical waveguide device 100 describedrelative to FIGS. 1 to 3, 4, and 5 can be modified to provide aconsiderable variation in its operation. For example, the opticalwaveguide device 100 can have a projected region of changeablepropagation constant 190 within the waveguide to provide one or more ofphase and/or amplitude modulation, optical deflection, opticalfiltering, optical attenuation, optical focusing, optical path lengthadjustment, variable phase tuning, variable diffraction efficiency,optical coupling, etc. As such, embodiments of many optical waveguidedevices that perform different operations are described in the followingsections along with the operations that they perform.

[0122] In each of the following embodiments of an optical waveguidedevice, the gate electrode is formed in a prescribed electrode shape toperform a desired optical operation. The projected region of changeablepropagation constant 190 assumes a shape similar to, but not necessarilyidentical to, the gate electrode. The shape of the region of changeablepropagation constant 190 within the waveguide can physically mapextremely closely to, with a resolution of down to 10 nm, the prescribedgate electrode shape. The construction and operation of differentembodiments of optical waveguide devices, and the operation, and effectsof various embodiments of regions of changeable propagation constant 190are described in this section.

[0123] 3A. Optical Modulator

[0124] This section describes an optical modulator, one embodiment ofoptical waveguide device 100 that modulates light passing through thewaveguide. The embodiments of optical waveguide device as shown in FIGS.1-3, 4, or 5 can perform either phase modulation or amplitude modulationof light passing through the waveguide. The modulation of light by theoptical waveguide device 100 can be optimized by reducing the losses inthe gate electrode 120 as well as reducing the charges in the 2DEG 108,while increasing the interaction of the waveguide mode with the 2DEG. Ingeneral, reducing the waveguide thickness h reduces the necessarywaveguide length L_(n) to produce modulation. Limiting the modulation ofthe 2DEG 108 also limits the effects on the free-carriers resulting fromabsorption during modulation. The length required for a specific loss,such as a 10 dB loss L_(10dB), can be experimentally determined for eachdevice. Both L_(N) and L_(10dB) are functions of Δq_(n). Δq_(n) dependson both the DC bias V_(g) as well peak-to-peak variation of the varyingAC signal v_(g).

[0125] To construct a high-speed modulator operating with bandwidth inexcess of, for example 50 GHz, it is important to consider both the RFmicrowave interfaces and the transit time of the free-carriers. Sincethe carriers arrive in the 2DEG either from the bulk electrode (notshown), from the first body contact electrode 118, or from the secondbody contact electrode 122, as the voltage of the gate electrode 122 ischanged, the time required for the voltage to equilibrate to supply aconstant voltage is, $\begin{matrix}{\tau_{e} = \frac{\left( {L/2} \right)}{v_{s}}} & 7\end{matrix}$

[0126] where v_(s) is the maximum velocity of the carriers and L is thechannel length illustrated in FIG. 1. Thus, the maximum length L of theMOS/HEMT structure of the optical waveguide device 100 is determined bythe requirement that τ_(e) be less than some percentage of the bitperiod.

[0127]FIG. 6 shows illustrative graph of the surface charge density andthe phase shift, both plotted as a function of the surface potential fora planar dielectric waveguide. In the FIG. 6 plot, the waveguide is anexemplary planar Si waveguide that has an electrical insulator layersuch as cladding on both the upper and lower surfaces. The waveguide isa single mode waveguide with the propagation constant of 14.300964 μm⁻¹.A change in the gate voltage by approximately 0.2-0.5 V results in achange to the surface charge density of the 2DEG by 8×10¹² cm⁻² which inturn will lead to a change of −0.01 in the propagation constant if the2DEG was due to electrons. Further assume that this 2DEG region iseffectively confined to within 5-50 nm adjacent the upper electricalinsulator layer, as is typical for MOS device physics. Assuming thatthere is an index change over only a 10 nm distance, the new propagationconstant is calculated to be 14.299792 μm⁻¹. The changes in thepropagation constant result in an additional phase shift of 180 degreesfor light travelling a length of 2.86 mm. Thus, gate voltage modulationleads to phase modulation of light in the waveguide. Similarly,free-carrier absorption occurs in the semiconductor locations wherethere are scattering centers (i.e. donor sites). Such free-carrierabsorption acts to modulate the amplitude of the propagating mode oflight. In general, amplitude modulation and phase shift modulation willoccur simultaneously, but one type of modulation can be arranged to bepredominant by controlling the doping profile of the waveguide.

[0128] In one embodiment, a channel waveguide is used to construct ahigh-speed modulator. With total internal reflection (TIR) using achannel waveguide, all the light within the waveguide is constrained tofollow the direction parallel to the optical path 101 since the lightthat contacts the electrical insulator layers 104, 110 of the waveguidereflects off the electrical insulator layers. Electrical insulatorlayers 104, 110 have a lower refractive index than the waveguide. Thechannel waveguide should be dimensioned to match the mode(s) of thewaveguide so the waveguide acts as a modulator for that mode.

[0129] The first body contact well 107 and the second body contact well109, that respectively interact with the first body contact electrode118 and the second body contact electrode 122, are both typicallyn-doped. This doping produces the body contact wells 107, 109 having alower refractive index than the silicon waveguide 106 due to thepresence of free-carriers. The body contact wells 107, 109 thus form alow-refractive index cladding that naturally confine the light mode(s)laterally within the waveguide 106. The body contact wells 107, 109 alsoabsorb some light passing through the waveguide 106, but the absorptionof light makes the waveguide lossy. Thus, it may be desired to use otherrefractive elements than the electrodes 118, 122 to confine the travelof the optical modes and limit the loss of the light.

[0130] For high speed modulation, the body contacts and the gateelectrodes can be made to act like a waveguide that operates at radiofrequencies. It is preferred, depending on the distance required, toproduce the required modulation to match the group velocity of theoptical wave to the microwave.

[0131] Variable optical attenuators are one additional embodiment ofoptical amplitude modulators. The description of constructing oneembodiment of variable optical attenuator using optical waveguidedevices is described later following a description of Bragg gratings.

[0132] 3B. Optical Deflectors

[0133] The FIG. 13 embodiment of the optical waveguide device 100 iscapable of acting as an optical deflector 1300 to controllably deflectlight passing through the waveguide. In one embodiment of deflector1300, the gate electrode 120 shown in the embodiments of FIGS. 1-3, 4,and 5 is physically and operationally divided into two electrodesincluding the input prism gate electrode 1304 and the output prism gateelectrode 1306. Both the input prism gate electrode 1304 and the outputprism gate electrode 1306 may be shaped in a trapezoidal or otherprismatic) configuration, and are both substantially co-planar andphysically positioned above the waveguide. When voltage of a firstpolarity is applied to one of the input prism gate electrode 1304 or theoutput prism gate electrode 1306 (not simultaneously), light will bedeflected from the incident axial direction of propagation into oppositelateral directions, e.g. respectively downwardly and upwardly within thewaveguide of FIG. 13. When a voltage of one polarity is applied to oneof the input prism gate electrode 1304, light will be deflected in theopposite lateral directions (upward or downward as shown in FIG. 13) aswhen voltage of the same polarity is applied to the output prism gateelectrode 1306.

[0134] The input prism gate electrode 1304 and the output prism gateelectrode 1306 are both formed from an electrically conductive materialsuch as metal. A first voltage supply 1320 extends between the combinedfirst body contact electrode 118 and second body contact electrode 122(that are electrically connected by substantially constant potentialconductor 204) and the input prism gate electrode 1304. A second voltagesupply 1322 extends between the combined first body contact electrode118 and second body contact electrode 122 to the output prism gateelectrode 1306. The first voltage supply 1320 and the second voltagesupply 1322 are individually controlled by the controller 201, andtherefore an opposite, or the same, or only one, or neither, polarityvoltage can be applied to the input prism gate electrode 1304 and theoutput prism gate electrode 1306. The input prism gate electrode 1304and the output prism gate electrode 1306 can be individually actuated sothat each one of the deflecting prism gate electrodes 1304, 1306 canproject a region of changeable propagation constant 190 in the waveguidewhile the other deflecting prism gate electrode does not. FIGS. 14 and15 show a shape of a embodiment of first region of changeablepropagation constant 190 a projected by the input prism gate electrode1304 closely maps that shape of the input prism gate electrode shown inFIG. 13. The shape of the FIGS. 14 and 15 embodiment of second region ofchangeable propagation constant 190 b projected by the output prism gateelectrode 1306 that closely maps that shape of the output prism gateelectrode 1306 shown in FIG. 13.

[0135] The input prism gate electrode 1304 has an angled surface 1308whose contour is defined by apex angle 1312. The output prism gateelectrode 1306 has an angled surface 1310 whose contour is defined byapex angle 1314. Increasing the voltage applied to either the inputprism gate electrode 1304 or the output prism gate electrode 1306increases the free carrier distribution in the region of the 2DEGadjacent the respective first region of changeable level of region ofchangeable propagation constant 190 a or the second region of changeablepropagation constant 190 b of the waveguide, shown in the embodiment ofFIG. 15 (that includes FIGS. 15A to 15D). Both regions of changeablepropagation constants 190 a, 190 b are prism (trapezoid) shaped andextend for the entire height of the waveguide and can be viewed as ahorizontally oriented planar prisms located in the waveguide whose shapein the plane parallel to the gate electrode is projected by therespective deflecting prism gate electrodes 1304, 1306. The waveguidevolume within either one of the regions of changeable propagationconstant 190 a, 190 b has a raised propagation constant compared tothose waveguide regions outside the region of changeable propagationconstant 190 a, 190 b. Additionally, a boundary is formed between eachone of the regions of changeable propagation constant 190 a, 190 b andthe remainder of the waveguide. The fact that each one of the regions ofchangeable propagation constant 190 a, 190 b has both a raisedpropagation constant level and a boundary makes the prism-shaped regionsof changeable propagation constant 190 a, 190 b act as, and indeed befunctionally equivalent to, optical prisms formed of eithersemiconductor material or glass.

[0136] As shown in FIG. 15A, when a level of voltage that isinsufficient to alter the carrier concentration is applied to eithergate electrode 1304 and 1306, no 2DEG 108 is established between theelectric insulator layer 110 and the waveguide 106. Since the 2DEGchanges the level of propagation constant in the respective regions ofpropagation constant 190 a, 190 b, no regions of changeable propagationconstants 190 a or 190 b are established in the waveguide 106.Therefore, the propagation constant of the first region of changeablepropagation constant 190 a in the waveguide matches the propagationconstant level of the remainder of the waveguide 106, and lighttravelling along paths 1420, 1422 continues to follow their incidentdirection. Path 1420 is shown with a wavefront 1440 while path 1422 isshown with a wavefront 1442

[0137] When voltage of a first polarity is applied to the input prismgate electrode 1304, the first region of changeable propagation constant190 a is projected in the shape of the input prism gate electrode 1304through the height of the waveguide to form the region of changedpropagation constant 190 a, as shown in FIG. 15B. The first region ofchangeable propagation constant 190 a thus functions as a variableoptical prism that can be selectively turned on and off. The firstregion of changeable propagation constant 190 is formed in thesemiconductor waveguide that deflects the light passing along thewaveguide along a path 1430 including wavefronts 1432. Individual beamsof the light following path 1430 are reflected with total internalreflectance between an upper and lower surface of the waveguide, but thedirection of travel of light within the waveguides remains along thepath 1430.

[0138] The intensity of the voltage applied to the input prism gateelectrode 1304 can be reduced to limit the propagation constant level ofthe region of changed propagation constant, so the light following path1420 would be deflected, e.g., along path 1436 instead of along path1430. The polarity of the voltage applied to the input prism gateelectrode 1304 can also be reversed, and light following path 1420 alongthe waveguide would be deflected to follow path 1438. Therefore, thedeflection of the light within the waveguide 106 can be controlled, andeven reversed, by controlling the voltage applied to the input prismgate electrode 1304. Changing of the propagation constant within thefirst region of changeable propagation constant 190 a causes suchdeflection by the input prism gate electrode 1304.

[0139] When no voltage is applied to the output prism gate electrode1306 as shown in FIGS. 15A and 15B, thereby effectively removing thesecond region of changeable propagation constant 190 b from thewaveguide 106. Light following within waveguide 106 along path 1422 isassumed to continue in a direction aligned with the incident light, orin a direction deflected by the input prism gate electrode 1304, sincethe propagation constant is uniform throughout the waveguide.

[0140] When voltage of a first polarity is applied to the output prismgate electrode 1306, the second region of changeable propagationconstant 190 b having a changed propagation constant level is projectedin the waveguide as shown in FIGS. 15C and 15D. The second region ofchangeable propagation constant 190 b may be viewed as an optical prismthat projects in the shape of output prism gate electrode 1306 to thewaveguide, thereby deflecting the light passing along the waveguidealong path 1460 with the wavefronts 1462 extending perpendicular to thedirection of travel.

[0141] The intensity of the voltage applied to the output prism gateelectrode 1306 shown in FIG. 15C can be reduced, so the light followingpath 1422 would be deflected at a lesser angle, e.g., along path 1466instead of along path 1460. Similarly, increasing the voltage applied tothe output prism gate electrode 1306 increases the angle of deflection.The polarity of the voltage applied to the output prism gate electrode1306 could also be reversed, and light following path 1420 within thewaveguide would be deflected in a reversed direction to the originalpolarity to follow path 1468. Therefore, the deflection of the lightwithin the waveguide 106 can be controlled, and even reversed, bycontrolling the voltage applied to the output prism gate electrode 1306.Additionally, the propagation constant in prescribed regions of thewaveguide, and the gate resistance, can be calibrated using thetechniques described in FIGS. 7 and 8 using the controller 201, themeter 205, and/or the temperature sensor 240.

[0142] The voltage being used to bias the input prism gate electrode1304 and/or the output prism gate electrode 1306 have the effect ofcontrollably deflecting the light as desired. The FIG. 14 embodiment ofoptical waveguide device 100 is structurally very similar to the FIGS. 1to 3 embodiment of optical waveguide device 100, however, the twoembodiments of optical waveguide devices perform the differing functionsof modulation and deflection.

[0143] In the FIG. 16 embodiment of optical waveguide device, theincident light flowing through the waveguide will be deflected from itsincident direction in a direction that is parallel to the axis of theoptical waveguide device. Such deflection occurs as result of variablevoltage applied between the second body contact electrode 122 and thefirst body contact electrode 118. In this configuration, an additionalvoltage source 1670 applies a voltage between the second body contactelectrode and the first body contact electrode to provide voltagegradient across the gate electrode. By varying the voltage between thesecond body contact electrode and the first body contact electrode, thelevel of propagation constant within the region of changeablepropagation constant changes. The voltage level applied to the waveguidethus causes a direction of the propagation of light flowing through thewaveguide to be controllably changes, leading to deflection of lightwithin the horizontal plane (e.g. upward and downward along respectivepaths 1672, 1674 as shown in FIG. 16).

[0144] The application of the first body contact-to-second body contactvoltage V_(SD) 1670 by the voltage source causes a propagation constantgradient to be established across the 2DEG in the waveguide 106 from thefirst body contact electrode to the second body contact electrode. Thus,the propagation constant, or the effective mode index, of the waveguide106, varies. This variation in the propagation constant leads to angledphase fronts from one lateral side of the waveguide to another. That is,the wavefront of the optical light flowing through the FIG. 16embodiment of waveguide 106 on one lateral side of the wavefront lagsthe wavefront on the other lateral side. The phase fronts of the lightemerging from the gate region will thus be tilted and the emerging beamwill be deflected by an angle γ. For a fixed V_(DS), the deflectionangle γ increases with the distance z traveled within the waveguide 106.The angle γ can be calculated by referring to FIG. 16 according to theequation. $\begin{matrix}{\gamma = {{a\quad {\tan \left( \frac{\Delta \quad O\quad P}{L} \right)}} = {{a\quad {\tan \left( \frac{\Delta \quad \overset{\_}{n}\quad W}{L} \right)}} = {{{a\quad {\tan \left( \frac{\overset{\_}{n}\quad {\cot (\theta)}{\Delta\theta}\quad W}{L} \right)}}\therefore\gamma} = {\left( \frac{W}{L} \right)10^{- 4}}}}}} & 8\end{matrix}$

[0145] Another embodiment of optical deflector 1700 is shown in FIG. 17.The waveguide 1702 is trapezoidal in shape. A gate electrode 1706 (thatis shown as hatched to indicate that the gate electrode shares the shapeof the waveguide 1702 in this embodiment) may, or may not, approximatethe trapezoidal shape of the waveguide. Providing a trapezoidal shapedwaveguide in addition to the shaped gate electrode enhances thedeflection characteristics of the optical deflector on light. In theoptical deflector 1700, if the voltage applied to the gate electrode isremoved, deflection occurs due to the shape of the waveguide due to thetrapezoidal shape of the waveguide. In this embodiment of opticalwaveguide device, the waveguide itself may be shaped similarly to theprior-art discrete optical prisms formed from glass.

[0146]FIG. 18 shows one embodiment of optical switch 1800 including aplurality of optical deflectors that each switches its input light fromone or more deflecting prism gate electrodes 1802 a through 1802 e toone of a plurality of receiver waveguides 1808 a to 1808 e. The opticalswitch 1800 includes an input switch portion 1802 and an output switchportion 1804. The input switch portion includes a plurality of the FIG.18 embodiment of deflecting prism gate electrodes as 1802 a to 1802 e.The deflecting prism gate electrodes 1802 a to 1802 e may each beconstructed, and operate, as described relative to one of the deflectingprism gate electrodes 1306, 1308 of FIG. 13. Each one of the deflectingprism gate electrodes 1802 a to 1802 e is optically connected at itsinput to receive light signals from a separate channel waveguide, notshown in FIG. 18. The output portion 1806 includes a plurality ofreceiver waveguides 1808 a, 1808 b, 1808 c, 1808 d, and 1808 e. Each ofthe receiver waveguides 1808 a to 1808 e is configured to receive lightthat is transmitted by each of the deflecting prism gate electrodes 1802a to 1802 e.

[0147] The optical switch 1800 therefore includes five deflecting prismgate electrodes 1802 a to 1802 e, in addition to five receiverwaveguides 1808 a to 1808 e. As such, the optical switch can operate as,e.g., a 5×5 switch in which any of the deflecting prism gate electrodes1802 a to 1802 e can deflect it's output light signal to any, or none,of the receiver waveguides 1808 a to 1808 e. Each of the deflectingprism gate electrodes 1802 a to 1802 e includes a gate portion that isconfigured with a respective angled apex surface 1810 a to 1810 e.Voltage supplied to any of the deflecting prism gate electrodes 1802 ato 1802 e results in an increase in the propagation constant within thecorresponding region of changeable propagation constant 190 (that formsin the waveguide below the corresponding deflecting prism gate electrode1802 a to 1802 e shown in FIG. 18) associated with that particulardeflecting prism's gate electrode.

[0148] Although the FIG. 18 embodiment of waveguide operates similarlyto the FIG. 15 embodiment of waveguide, if no voltage is applied to anyparticular deflecting prism gate electrode 1802 a to 1802 e, then thelight travels directly through the waveguide associated with thatdeflecting prism gate electrode and substantially straight to arespective receiver waveguide 1808 a to 1808 e located in front of thatdeflecting prism gate electrode. The apex angles 1810 a and 1810 e(and/or the angles of the waveguide as shown in the FIG. 17 embodiment)of the outer most deflecting prism gate electrodes 1802 a and 1802 e areangled at a greater angle than deflecting prism gate electrodes 1802 b,1802 c, and 1802 d. An increase in the apex angle 1810 a and 1810 eallows light flowing through the waveguide to be deflected through agreater angle toward the more distant receivers 1808 a to 1808 e. It mayalso be desired to minimize the lateral spacing between each successivedeflecting prism gate electrode 1802 a to 1802 e, and the lateralspacing between each respective receiver 1808 a to 1808 e to minimizethe necessary deflection angle for the deflecting prism gate electrodes.The apex angle of those deflecting prism gate electrodes that aregenerally to the left of an axial centerline of the optical switch (andthus have to deflect their light to the right in most distances) areangled oppositely to the apex angle of those deflecting prism gateelectrodes that are to the right of the centerline of that switch thathave to deflect their light to the left in most instances. Deflectingprism gate electrodes 1802 b, 1802 c, and 1802 d that have otherdeflecting prism gate electrodes locate to both their right and leftshould also have receivers located both to their right and left as shownin FIG. 18 and therefore must be adapted to provide for deflection oflight to either the left or right. For example, the deflecting prismgate electrode 1802 c must cause light traveling through its waveguideto be deflected to the right when transmitting its signal to thereceivers 1808 d or 1808 e. By comparison, the deflecting prism gateelectrode 1802 c must cause light that is passing through its waveguideto be deflected to its left when deflecting light to receivers 1808 aand 1808 b.

[0149] Optical switch 1800 has the ability to act extremely quickly,partly due to the fact that each deflecting prism gate electrode has nomoving parts. Each of the deflecting prism gate electrodes 1802 a to1802 e can be adjusted and/or calibrated by controlling the voltageapplied to that deflecting prism gate electrode using the techniquesdescribed in FIGS. 7 and 8. Applying the voltage to the deflecting prismgate electrodes 1802 a to 1802 e results in an increase, or decrease(depending on polarity), of the propagation constant level of the regionof changeable propagation constant in the waveguide associated with thatdeflecting prism gate electrode 1802 a to 1802 e.

[0150]FIG. 19 shows another embodiment of optical switch 1900. Theoptical switch includes a concave input switch portion 1902 and aconcave output switch portion 1904. The input switch portion 1902includes a plurality of deflecting prism gate electrodes 1902 a to 1902d (having respective apex angles 1910 a to 1910 d) that operatesimilarly to the FIG. 18 embodiment of deflecting prism gate electrodes1802 a to 1802 e. Similarly, the concave output switch portion 1902includes a plurality of receivers 1908 a to 1908 d. Each one of thereceivers 1908 a to 1908 d operates similarly to the FIG. 18 embodimentof receivers 1808 a to 1808 e. The purpose of the concavity of theconcave input switch deflector portion 1902 and the concave outputportion 1904 is to minimize the maximum angle through which any one ofthe optical deflecting prism gate electrodes has to deflect light toreach any one of the receivers. This is accomplished by mounting each ofthe optical deflecting prism gate electrodes at an angle that bisectsthe rays extending to the outermost receivers 1908 a to 1908 d. Themounting of the optical deflecting gate electrodes also generallyenhances the reception of light by the receivers since each receiver isdirected at an angle that more closely faces the respective outermostoptical deflecting prism gate electrodes. The operation of theembodiment of optical switch 1900 in FIG. 19 relative to the deflectingprism gate electrodes 1902 a to 1902 d and the receivers 1908 a and 1908d is similar to the above-described operation of the optical switch 1800in FIG. 18 relative to the respective deflecting prism gate electrodes1802 a to 1808 e (except for the angle of deflection of the deflectingprism gate electrode).

[0151] 3C. Optical Gratings

[0152] Bragg Gratings in the dielectric slab waveguide as well as infibers are well known to perform various optical functions such asoptical filtering, group velocity dispersion control, attenuation, etc.The fundamental principle behind Bragg grating is that small, periodicvariation in the mode index or the propagation constant leads toresonant condition for diffraction of certain wavelengths.

[0153] These wavelengths satisfy the resonant condition for build up ofdiffracted power along certain direction. The wavelength selectivitydepends on the design of the grating structure. In the case presentedhere, we envision a Bragg grating that is electrically controlled viathe effect of 2DEG. There are many ways to produce the undulatingpattern in 2DEG. The methods include: undulation in the effectivedielectric constant of the gate insulator, patterned gate metal,periodic doping modulation etc. FIG. 20 is one example. In FIG. 20 thegate dielectric is divided into two gate insulators of differentdielectric strength.

[0154] FIGS. 20 to 22 show a variety of embodiments of optical Bragggratings in which the shape or configuration of the gate electrode 120of the optical waveguide device 106 is slightly modified. Bragg gratingsperform a variety of functions in optical systems involving controllableoptical refraction as described below. In the different embodiments ofoptical Bragg gratings, a series of planes of controllable propagationconstant (compared to the surrounding volume within the waveguide) areprojected into the waveguide 106. The planes of controllable propagationconstant may be considered to form one embodiment of a region ofchangeable propagation constant 190, similar to those shown anddescribed relative to FIGS. 1-3, 4, or 5. In the FIG. 20 embodiment ofoptical Bragg grating 2000, the second insulator layer 110 is providedwith a corrugated lower surface 2002. The corrugated lower surfaceincludes a plurality of raised lands 2004 that provide a variablethickness of the second insulator layer 110 between different portionsof the corrugated lower surface of the second electrical insulator layeror oxide 110 and the gate electrode 120. Each pair of adjacent raisedlands 2004 are uniformly spaced for one Bragg grating.

[0155] A distance T1 represents the distance between the raised lands2004 of the corrugated surface 2002 and the gate electrode 120. Adistance T2 represents the distance from the lower most surface of thecorrugated surface 2002 and the gate electrode 122. Since the distanceT1 does not equal T2, the electrical field at theinsulator/semiconductor interface of the second insulator layer 110 fromthe gate electrode to the waveguide 106 will vary along the length ofthe waveguide. For example, a point 2006 in the waveguide that isunderneath the location of one of the raised lands 2004 experiences lesselectrical field at the insulator/semiconductor interface to voltageapplied between the gate electrode and the waveguide than point 2008that is not underneath the location of one of the raised lands. Sincethe resistance of the second insulator layer 110 in the verticaldirection varies along its length, the resistance between the gateelectrode and the waveguide (that has the second insulating layerinterspersed there between) varies along its length. The strength of theelectric field applied from the gate electrode into the waveguide variesas a function of the thickness of the second insulator layer 110. Forexample, the projected electric field within the waveguide at point 2006exceeds the projected electric field at point 2008. As such, theresultant free carrier charge distribution in the 2DEG above point 2006exceeds the resultant free carrier charge distribution in the 2DEG abovepoint 2008. Therefore, the resultant propagation constant in theprojected region of changeable propagation constant 190 in the waveguideat point 2006 exceeds the resultant propagation constant in theprojected region of changeable propagation constant 190 in the waveguideat point 2008.

[0156] The raised lands 2004 are typically formed as grooves in thesecond insulator layer 110 that extend substantially perpendicular to,or angled relative to, the direction of light propagation within thewaveguide. The raised lands 2004 may extend at a slight angle asdescribed with respect to FIG. 23 so that reflected light passingthrough the waveguide may be deflected at an angle to, e.g., anotherdevice. A low insulative material 2010 is disposed between the secondelectrical insulator layer 110 and waveguide 106. The previouslydescribed embodiments of optical waveguide devices relied on changes inthe planar shape of the gate electrode to produce a variable region ofchangeable propagation constant 190 across the waveguide. The FIGS. 20to 22 embodiments of optical waveguide devices rely on variations ofthickness (or variation of the electrical resistivity of the material)of the gate electrode, or the use of an insulator under the gateelectrode, to produce a variable propagation constant across thewaveguide.

[0157] Since a variable electromagnetic field is applied from the gateelectrode 120 through the second electrical insulator layer or oxide 110to the waveguide 106, the propagation constant of the waveguide 106 willvary. The carrier density in the 2DEG 108 will vary between the locationin the 2DEG above the point 2006 and above the point 2008. Moreparticularly, the lower resistance of the second electrical insulatorlayer or oxide at point 2006 that corresponds to distance T1 will resultin an increased carrier density compared to the point 2008 on the 2DEGthat corresponds to an enhanced distant T2, and resulting in anincreased resistance of the 2DEG. Such variation in the propagationconstant along the length of the waveguide 106 results only when gateelectrode 120 is actuated. When the gate electrode is deactivated, thepropagation constant across the waveguide 106 is substantially uniform.In the FIGS. 20 to 22 embodiments of optical gratings, the propagationconstant is changed by the thickness of the gate electrode, i.e., theraised lands locations. Therefore, this embodiment of optical waveguidedevice changes the propagation constant by changing the thickness of thegate electrode to form the Bragg gratings, not by changing the shape ofthe gate electrode.

[0158] Such a variation in propagation constant within certain regionsat the waveguide 106 will result in some percentage of the lighttraveling along the waveguide 106 to be reflected. The variation in thepropagation constant extends substantially continuously across thelength of the FIG. 20 embodiment of waveguide 106. As such, even thougha relatively small amount of energy of each light wave following adirection of light travel 101 will be reflected by each plane projectedby a single recess, a variable amount of light can be controllablyreflected by the total number of planes 2012 in each Bragg grating. Thedistance d in the direction of propagation of light between successiveplanes within the Bragg grating is selected so that the lightwavesreflected from planes 2012 are in phase, or coherent, with the lightreflected from the adjacent planes. The strength of the 2DEG determinesthe reflectivity or the diffraction efficiency of the Bragg structure.By varying the strength, we may chose to control the light diffracted bythe Bragg structure. This will be useful in construction of theattenuators, modulators, switches etc.

[0159] The lightwaves travelling in direction 101 from the adjacentphase planes 2012 will be in phase, or coherent, for a desired light ofwavelength λ if the difference in distance between light reflected fromsuccessive planes 2012 equals an integer multiple of the wavelength ofthe selected light. For example, light traveling along the waveguide 106(in a direction from left to right as indicated by the arrow inwaveguide 106) that is reflected at the first plane 2012 (the planefarthest to the left in FIG. 20) is reflected either along the waveguide106 or at some angle at which the reflected light beam is deflected, andtravels some distance shorter than light reflected off the next plane(the first plane to the right of the leftmost plane 2012 in FIG. 20).

[0160] Light reflected from the Bragg gratings of the waveguide will bein-phase, or coherent, when the distance d between recesses taken in adirection parallel to the original direction of propagation of the lightin the waveguide is an integer multiple of a selected bandwidth oflight. In the FIG. 23 embodiment of Bragg grating, light reflected offsuccessive planes 2311 would coherently add where the distance “d” issome integer multiple of the wavelength of the reflected light. Theother wavelengths of light interfere destructively, and cannot bedetected by a detector.

[0161] The FIG. 21 embodiment of Bragg grating 2100 includes a pluralityof insulators 2102 evenly spaced between the electrical insulator layer110 and the waveguide 106. The electrical resistance of the insulators2102 differs from that of the electrical insulator layer 110.Alternatively, inserts could be inserted having a different electricalresistance than the remainder of the electrical insulator layer. Theinsulator 2102 limits the number of carriers that are generated in thoseportions of the 2DEG 108 below the insulators 2102 compared to thoselocations in the 2DEG that are not below the insulators 2102. As such,the propagation constant in those portions of the waveguide 106 that arebelow the insulators 2102 will be different than the propagationconstant in those portions of the waveguide that are not below theinsulators 2102. Planes 2112 that correspond to the regions of changedpropagation constant within the waveguide under the insulators that areprojected into the waveguide 106. Such planes 2112 are thereforeregularly spaced since the location of the projected regions ofchangeable propagation constant corresponds directly to the location ofthe insulators 2102. The insulator properties that control the strengthof the electric field at the insulator/semiconductor interface are dueto its dielectric constant at the modulation frequencies of interest.The insulator may have variable dielectric constant at radio frequenciesbut is substantially unchanged at the optical frequencies. Thus, opticalwave does not “see” the undulation unless induced by 2DEG.

[0162] In the FIG. 22 embodiment of optical Bragg grating 2200, anothershape of regularly shaped patterning, that may take the form ofcorrugated patterns along the bottom surface of the gate electrode 120,is formed in the gate electrode 120. The optical Bragg grating 2200includes a series of raised lands 2202 formed in the lower surface theof the metal gate electrode 120. These raised lands 2202 may be angledrelative to the waveguide for a desired distance. The raised lands 2202in the gate electrode are configured to vary the electrical field at theinsulator/semiconductor interface to the waveguide 106 in a patterncorresponding to the arrangement of the raised lands 2202. For example,the propagation constant will be slightly less in those regions of thewaveguide underneath the raised lands 2202 than in adjacent regions ofthe waveguide since the distance that the raised lands 2202 areseparated from the waveguide is greater than the surrounding regions.

[0163] In this disclosure, Bragg gratings may also be configured using aSAW, or any other similar acoustic or other structure that is configuredto project a series of parallel planes 2112 representing regions ofchangeable propagation constant into the waveguide 106.

[0164] The planes 2311 are each angled at an angle a from the directionof propagation of the incident light 2304. As such, a certain amount oflight is reflected at each of the planes 2311, resulting in reflectedlight 2306. The majority of light 2304 continues straight through thewaveguide past each plane 2311, with only a relatively minor portionbeing reflected off each plane to form the reflected light 2306. Thedifference in distance traveled by each successive plane 2311 thatreflects light is indicated, in FIG. 23, by the distance d measured in adirection parallel to the incident light beam 2304. Therefore, distanced is selected to be some multiple of the wavelength of the light that isto be reflected from the FIG. 23 embodiment of optical Bragg grating.The selected wavelength λ of light that reflect off successive planesspaced by the distance d must satisfy the equation:

2 sin α=λ/d  9

[0165] If each reflected light path 2306 distance varies by an integermultiple of the wavelength of the selected light, the light at thatselected wavelength will constructively interfere at a detector 2312 andthus be visible. The detector can be any known type of photodetector.Since the distance d has been selected at a prescribed value, thedistance of each ray of reflected light 2306 off each plane travels aslightly greater distance than a corresponding ray of light reflectedoff the preceding plane (the preceding plane is the plane to the left asshown in FIG. 23). Those wavelengths of light that are not integermultiples of the distance d, will interfere destructively and thus notbe able to be sensed by the detector 2312.

[0166] The Bragg gratings represent one embodiment of a one-dimensionalperiodic structure. More complicated optical functions may be achievedby using a two dimensional periodic patterns. One embodiment of atwo-dimensional periodic structure that corresponds to the Bragg gratingincludes using a “polka dot” pattern, in which the reflectivity of aparticular group of wavelengths are unity in all directions in theplane. A “line defect” in the pattern may be provided that results inthe effective removal of one or more of these “polka dots” along a linein a manner that causes guiding of light along the line defect. Manygeometrical shapes can be used in addition to circles that form thepolka dot patter. All of these can be achieved by generalization of theBragg gratings discussed in detail above to the one-dimensionalpatterns.

[0167]FIG. 23 shows one embodiment of optical Bragg grating 2303 that isconfigured to diffract light. A series of such optical Bragg gratingslabeled as 2303 a to 2303 e can be applied to the FIG. 24 embodiment ofwaveguide. The specific optical Bragg grating 2303 relating to a desiredwavelength λ of light can be actuated, while the remainder of theoptical Bragg gratings 2303 are deactivated. One design may provide aplurality of optical Bragg gratings 2303 arranged serially along achannel waveguide, with only a minimal difference between thewavelengths λ of the reflected light by successive optical Bragggratings 2303 a to 2303 e. For example, the first optical Bragg grating2303 a reflects light having a wavelength Al that exceeds the wavelengthλ₂ of the light that is diffracted by the second optical grating 2303 b.Similarly, the wavelength of light that can be reflected by each opticalBragg grating is greater than the wavelength that can be reflected bysubsequent Bragg gratings. To compensate for physical variations in thewaveguide (resulting from variations in temperature, device age,humidity, or vibrations, etc.), a Bragg grating that corresponds to adesired wavelength of reflected light may be actuated, and then thereflected light monitored as per wavelength. If multiple optical Bragggratings are provided to allow for adjustment or calibration purposes,then the differences in spacing between successive planes of thedifferent optical Bragg gratings is initially selected. If it is foundthat the actuated Bragg grating does not deflect the desired light (thewavelength of the deflected light being too large or too small), thenanother optical Bragg grating (with the next smaller or larger planespacing) can then be actuated. The selection of the next Bragg gratingto actuate depends upon whether the desired wavelength of the firstactuated optical Bragg grating is more or less than the wavelength ofthe diffracted light. This adjustment or calibration process can beperformed either manually or by a computer using a comparison program,and can be performed continually during normal operation of an opticalsystem employing optical Bragg gratings.

[0168]FIG. 25 shows one embodiment of Echelle grating 2500. The Echellegrating 2500 may be used alternatively as a diffraction grating or alens grating depending on the biasing of the gate electrode. The Echellegrating 2500 is altered from the FIGS. 1 to 3 and 5 embodiment ofoptical waveguide device 100 by replacing the rectangular gate electrodeby a triangular-shaped Echelle gate electrode 2502. The Echelle-shapedgate electrode 2502 includes two parallel sides 2504 and 2506 (side 2506is shown as the point of the triangle, but actually is formed from alength of material shown in FIG. 26 as 2506), a base side 2510, and aplanar grooved surface 2512.

[0169] The base surface 2510 extends substantially perpendicular to theincident direction of travel of light (the light is indicated by arrows2606, 2607, and 2609 shown in FIG. 26) entering the Echelle grating. Thegrooved side 2512 is made of a series of individual grooves 2515 thatextend parallel to the side surface, and all of the grooves regularlycontinue from side 2504 to the other side 2506. Each groove 2515includes a width portion 2519 and rise portion 2517.

[0170] The rise portion 2517 defines the difference in distance thateach individual groove rises from its neighbor groove. The rise portion2517 for all of the individual grooves 2515 are equal, and the riseportion 2517 equals some integer multiple of the wavelength of the lightthat is to be acted upon by the Echelle grating 2500. Two exemplaryadjacent grooves are shown as 2515 a and 2515 b, so the verticaldistance between the grooves 2515 a and 2515 b equals 2517. The widthportion 2519 of the Echelle shape gate electrode 2502 is equal for allof the individual grooves. As such, the distance of the width portion2519 multiplied by the number of individual grooves 2515 equals theoperational width of the entire Echelle shaped gate electrode.Commercially available three dimensional Echelle gratings that areformed from glass or a semiconductor material have a uniform crosssection that is similar in contour to the Echelle shaped gate electrode2502. The projected region of changeable propagation constant 190 can beviewed generally in cross-section as having the shape and dimensions ofthe gate electrode (including grooves), and extending vertically throughthe entire thickness of the waveguide 106. The numbers of individualgrooves 2515 in the FIG. 25 embodiment of Echelle shaped gate electrode2502 may approach many thousand, and therefore, the size may becomerelatively small to provide effective focusing.

[0171]FIG. 26 shows the top cross sectional view of region of changeablepropagation constant 190 shaped as an Echelle grating 2500. Thewaveguide 106 is envisioned to be a slab waveguide, and is configured topermit the angular defraction of the beam of light emanating from theEchelle grating 2500. When voltages are applied to the FIG. 25embodiment of Echelle shaped gate electrode 2502, a projected region ofchangeable propagation constant 190 of the general shape shown in FIG.26 is established within the waveguide 106. Depending upon the polarityof the applied voltage to the Echelle shaped gate electrode in FIG. 25,the propagation constant within the projected region of changeablepropagation constant 190 can either exceed, or be less than, thepropagation constant within the waveguide outside of the projectedregion of changeable propagation constant 190. The relative level ofpropagation constants within the projected region of changeablepropagation constant 190 compared to outside of the projected region ofchangeable propagation constant determines whether the waveguide 106acts to diffract light or focus light. In this section, it is assumedthat the voltage applied to the gate electrode is biased so the Echellegrating acts to diffract light, although equivalent, techniques wouldapply for focusing light, and are considered a part of this disclosure.

[0172] In FIG. 26, three input light beams 2606, 2607, and 2609 extendinto the waveguide. The input light beams 2606, 2607, and 2609 are shownas extending substantially parallel to each other, and alsosubstantially parallel to the side surface 2520 of the projected regionof changeable propagation constant 190. The projected region ofchangeable propagation constant 190 as shown in FIG. 26 preciselymirrors the shape and size of the FIG. 25 embodiment of Echelle shapedgate electrode 2502. As such, the projected region of changeablepropagation constant 190 can be viewed as extending vertically throughthe entire thickness of the waveguide 106. The numbers of individualgrooves 2515 in the FIG. 25 embodiment of Echelle shaped gate electrode2502 may approach many thousand to provide effective diffraction, andtherefore, individual groove dimensions are relatively small. It istherefore important that the projected region of changeable propagationconstant 190 precisely maps from the Echelle shaped gate electrode 2502.

[0173] Three input beams in 2606, 2607, and 2609 are shown entering theprojected region of changeable propagation constant 190, each containingmultiple wavelengths of light. The three input beams 2606, 2607, and2609 correspond respectively with, and produce, three sets of outputbeams 2610 a or 2610 b; 2612 a, 2612 b or 2612 c; and 2614 a or 2614 bas shown in FIG. 26. Each diffracted output beam 2610, 2612, and 2614 isshown for a single wavelength of light, and the output beam representsthe regions in which light of a specific wavelength that emanate fromdifferent grooves 2604 will constructively interfere. In otherdirections, the light destructively interferes.

[0174] The lower input light beam 2606 that enters the projected regionof changeable propagation constant 190 travels for a very short distanced1 through the projected region of changeable propagation constant 190(from the left to the right) and exits as output beam 2610 a or 2610 b.As such, though the region of changeable propagation constant 190 has adifferent propagation constant then the rest of the waveguide 106, theamount that the output beam 2610 a, or 2610 b is diffracted is verysmall when compared to the amount of diffraction of the other outputbeams 2612, 2614 that have traveled a greater distance through theprojected region of changeable propagation constant 190.

[0175] The middle input light beam 2607 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the Echelle grating. If there is novoltage applied to the gate electrode, then the output light will beunaffected by the region of changeable propagation constant 190 as thelight travels the region, and the direction of propagation for lightfollowing input path 2607 will be consistent within the waveguide along2612 a. If a voltage level is applied to the FIG. 25 embodiment of gateelectrode 2502, then the propagation constant within the region ofchangeable propagation constant 190 is changed from that outside theregion of changeable propagation constant. The propagation constant inthe region of changeable propagation constant 190 will thereupondiffract light passing from the input light beam 2607 through an angleθ_(d1) along path 2612 b. If the voltage is increased, the amount ofdiffraction is also increased to along the path shown at 2612 c.

[0176] Light corresponding to the input light beam 2609 will continuestraight along line 2614 a when no voltage is applied to the gateelectrode. If a prescribed level of voltage is applied to the gateelectrode, the output light beam will be diffracted through an outputangle θ_(d2) along output light beam 2614 b. The output angle θ_(d2) ofoutput diffracted beam 2614 b exceeds the output angle θ_(d1) ofdiffracted beam 2612 b. The output angle varies linearly from one sidesurface 2522 to the other side surface 2520, since the output angle is afunction of the distance the light is travelling through the projectedregion of changeable propagation constant 190.

[0177] When the Echelle grating diffracts a single wavelength of lightthrough an angle in which the waves are in phase, the waves of thatlight constructively interfere and that wavelength of light will becomevisible at that location. Light of different wavelength will notconstructively interfere at that same angle, but will at some otherangle. Therefore, in spectrometers, for instance, the location thatlight appears relates to the specified output diffraction angles of thelight, and the respective wavelength of the light within the light beamthat entered the spectrometer.

[0178]FIG. 27 shows one embodiment of Echelle grating 2700 that isconfigured to reflect different wavelengths of light (instead ofdiffracting light) through an output reflection angle. For instance, aninput light beam 2702 of a prescribed wavelength, as it contacts agrating surface 2704 of a projected Echelle grating 2706, will reflectan output light beam 2708 through an angle. The propagation constant ofthe region of changeable propagation constant 190 will generally have tobe higher than that for a diffraction Echelle grating. In addition, theangle at which the grating surface 2704 faces the oncoming input lightbeam 2702 would probably be lower if the light is refracted, notreflected. Such design modifications can be accomplished byreconfiguring the shape of the gate electrode in the optical waveguidedevice. Shaping the gate electrodes is relatively inexpensive comparedwith producing a distinct device.

[0179] 3D Optical Lenses

[0180] Waveguide lenses are important devices in integrated opticalcircuits because they can perform various essential functions such asfocusing, expanding, imaging, and planar waveguide Fourier Transforms.

[0181] The FIG. 25 embodiment of Echelle grating 2500 can be used notonly as a diffraction grating as described relative to FIG. 26, but thesame structure can also be biased to perform as a lens to focus light.To act as a lens, the polarity of the voltage of the Echelle grating2500 applied between the gate electrode and the combined first bodycontact/second body contact electrodes is opposite that shown for theFIGS. 26 embodiment of diffraction grating.

[0182]FIGS. 28 and 29 show three input light beams that extend into theregion of altered propagation constant 190 in the waveguide are shown as2806, 2807, and 2809. parallel to each other, and also substantiallyparallel to the side surfaces 2520, 2522 of the projected region ofchangeable propagation constant 190. The projected region of changeablepropagation constant 190 shown in FIGS. 28 and 29 generally mirrorsvertically through the height of the waveguide the shape and size of theFIG. 25 embodiment of Echelle shaped gate electrode 2502.

[0183] The light input from the input beams 2806, 2807, and 2809 extendthrough the region of changeable propagation constant 190 to form,respectively, the three sets of output beams 2810 a and 2810 b; 2812 a,2812 b and 2812 c; and 2814 a and 2814 b as shown in FIG. 28. Eachfocused output beam 2810, 2812, and 2814 is shown for a singlewavelength of light, and the output beam represents the direction oftravel of a beam of light of a specific wavelength in which that beam oflight will constructively interfere. In other directions, the light ofthe specific wavelength destructively interferes.

[0184] The lower input light beam 2806 that enters near the bottom ofthe projected region of changeable propagation constant 190 travels fora very short distance dl through the projected region of changeablepropagation constant 190 (as shown from the left to the right) and exitsas output beam 2810 a or 2810 b. As such, though the region ofchangeable propagation constant 190 has a different propagation constantthen the rest of the waveguide 106. The amount that the output beam 2810a is focused is very small when compared to the amount of focusing onthe other output beams 2812, 2814 that have traveled a greater distancethrough the region of changeable propagation constant 190.

[0185] The middle input light beam 2807 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the projected Echelle grating. If thereis no voltage applied to the gate electrode, then the output light willbe unaffected by the region of changeable propagation constant 190, andlight following input path 2807 will continue straight after exiting thewaveguide along 2812 a. If a medium voltage level is applied to the gateelectrode, then the propagation constant within the region of changeablepropagation constant 190 will not equal that within the surroundingwaveguide. The propagation constant in the region of changeablepropagation constant 190 will deflect light beam 2807 through an angleθ_(f1) along path 2812 b. If the voltage is increased, the amount ofdeflection for focusing is also increased to the angle shown at 2812 c.

[0186] Light corresponding to the input light beam 2809 will continuestraight through the region of changeable propagation constant alongline 2814 a when no voltage is applied to the gate electrode. If aprescribed level of voltage is applied to the gate electrode, the outputlight beam will be focused through an output angle θ_(f2) to alongoutput light beam 2814 b. The output angle θ_(f2) of output focused beam2814 b exceeds the output angle θ_(f1) of focused beam 2812 b if thesame voltage applied to the gate electrode. The output angle varieslinearly from one side surface 2522 to the other side 2520, since theoutput angle is a function of the distance the light is travellingthrough the projected region of changeable propagation constant 190.

[0187]FIGS. 28 and 29 demonstrate that a voltage can be applied to anEchelle shaped gate electrode 2602, and that it can be biased in amanner to cause the Echelle grating 2500 to act as a focusing device.The level of the voltage can be varied to adjust the focal length. Forexample, assume that a given projected region of changeable propagationconstant 190 results in the output focused beams 2810, 2812, and 2814converging at focal point f_(p1). Increasing the gate voltage will causethe propagation constant in the projected region of changeablepropagation constant 190 to increase, resulting in a correspondingincrease in the output focus angle for each of the output focused beams.As such, the output focus beams would converge at a different point,e.g., at focal point f_(p2), thereby, effectively decreasing the focallength of the lens. The FIGS. 28 and 29 embodiment of focusing mechanismcan be used in cameras, optical microscopes, copy machines, etc., or anydevice that requires an optical focus. There are no moving parts in thisdevice, which simplifies the relatively complex auto focus devices thatare presently required for mechanical lenses. Such mechanical autofocuslenses, for example, require precisely displacing adjacent lenses towithin a fraction of a wavelength.

[0188]FIG. 30 shows another embodiment of an optical waveguide device100 including a Bragg grating 3008 that is used as a lens to focus lightpassing through the waveguide. The embodiment of optical waveguidedevice 100, or more particularly the FIG. 2 embodiment of gate electrodeof the optical waveguide device, is modified by replacing the continuousgate electrode (in FIG. 2) with a discontinuous electrode in the shapeof a Bragg grating (shown in FIG. 30). The Bragg grating 3008 is formedwith a plurality of etchings 3010 that each substantially parallels theoptical path 101 of the optical waveguide device. In the FIG. 30embodiment of Bragg grating 3008, the thickness' of the successiveetchings to collectively form gate electrode 120 increase toward thecenter of the optical waveguide device, and decreases toward the edges120 a, 120 b of the gate electrode 120. Therefore, the region ofchangeable propagation constant 190 in the waveguide is thicker at thoseregions near the center of the waveguide. Conversely, the region ofchangeable propagation constant 190 becomes progressively thinner atthose regions of the waveguide near edges 120 a, 120 b. The propagationconstant is a factor of both the volume and the shape of the materialused to form the gate electrode. The propagation constant is thus higherfor those regions of changeable propagation constant closer to thecenter of the waveguide.

[0189] Light is assumed to be entering the waveguide 106 followingsubstantially parallel paths as shown by exemplary paths 3012 a and 3012b. Paths 3012 a and 3012 b represent two paths travelling at theoutermost positions of the waveguide. The locations between paths 3012 aand 3012 b are covered by a continuum of paths that follow similarroutes. When sufficient voltage is applied to the Bragg grating shapedelectrode, the light following paths 3012 a and 3012 b will be deflectedto follow output paths 3014 a and 3014 b, respectively. Output paths3014 a and 3014 b, as well as the paths of all the output paths thatfollow through the waveguide under the energized Bragg grating 3008 willbe deflected a slightly different amount, all toward a focus point 3016.The FIG. 30 embodiment of optical waveguide device therefore acts as alens. The Bragg grating 3008, though spaced a distance from thewaveguide, can be biased to direct the light in a manner similar to alens.

[0190] The reason why the embodiment of Bragg grating shown in FIG. 30acts as a lens is now described. Light travelling within the waveguiderequires a longer time to travel across those regions of changeablepropagation constant at the center (i.e., taken vertically as shown inFIG. 30) than those regions adjacent the periphery of the lens (i.e.,near edges 120 a, 120 b). This longer time results because thepropagation constant is greater for those regions near the center. Forlight of a given wavelength, light exiting the lens will meet at aparticular focal point. The delay imparted on the light passing throughthe regions of changeable propagation constant nearer the center of thelens will be different from that of the light passing near edges 120 a,120 b. The total time required for the light to travel to the focalpoint is made up from the combination of the time to travel through theregion of changeable propagation constant 190 added to the time totravel from the region of changeable propagation constant 190 to thefocal point. The time to travel through the region of changeablepropagation constant 190 is a function of the propagation constant ofeach region of changeable propagation constant 190. The time to travelfrom the region of changeable propagation constant 190 to the focalpoint is a function of the distance from the region of changeablepropagation constant 190 to the focal point. As a result of thevariation in propagation constant from the center of the waveguidetoward the edges 120 a, 120 b, a given wavelength of light arrives at afocal point simultaneously, and the lens thereby focuses light.

[0191] There has been increasing interest in waveguide lenses such asFresnel lenses and grating lenses. Such lenses offer limited diffractionperformance, and therefore they constitute a very important element inintegrated optic devices. Waveguide Fresnel lenses consist of periodicgrating structures that cause a spatial phase difference between theinput and the output wavefronts. The periodic grating structure gives awavefront conversion by spatially modulating the grating. Assuming thatthe phase distribution function of the input and output waves aredenoted by φ₁ and φ₂, respectively, the phase difference Δφ in theguided wave structure can be written as:

Δφ=φ₀−φ_(I)  10

[0192] The desired wavefront conversion is achieved by a given phasemodulation to the input wavefront equal to Δφ. The grating for suchphase modulation consists of grating lines described by:

Δφ=2mπ  11

[0193] where m is an integer, and, for light having a specificwavelength, the light from all of the grating lines will interfereconstructively.

[0194] The phase difference Δφ for a planar waveguide converging wavefollows the expression:

Δφ(x)=kn _(eff)(ƒ−{square root}{square root over (x ²+ƒ²)})  12

[0195] where ƒ is the focal length, n_(eff) is the propagation constantof the waveguide, and x is the direction of the spatial periodic gratingmodulation.

[0196]FIGS. 30 and 31 show two embodiments of optical waveguide devicesthat perform waveguide Fresnel lens functions. The two-dimensionalFresnel lenses follow the phase modulation like their three-dimensionallens counterpart:

φ_(F)(x)=Δφ(x)+2mπ  13

[0197] for x_(m)<|x|21 x_(m+1), the phase modulation Δφ(x_(m))=2mπ,which is obtained by segmenting the modulation into Fresnel zones sothat φ_(F)(x) has amplitude 2π. Under the thin lens approximation, thephase shift is given by KΔnL. Therefore, the phase of the wavefront fora specific wavelength can be controlled by the variations of Δn and L.If Δn is varied as a function of x, where the lens thickness, L, is heldconstant, as shown in FIG. 30, it is called the GRIN Fresnel lens and isdescribed by:

Δn(x)=Δn _(max)(φ_(F)(x)/2π+1)  14

[0198]FIG. 32 shows one embodiment of optical waveguide device thatoperates as a gradient-thickness Fresnel lens where Δn is held constant.The thickness of the lens L has the following functional form:

L(x)=L_(max)(φ_(F)(x)/2π+1)  15

[0199] To have 2π phase modulation, in either the FIG. 30 or FIG. 31embodiment of lens, the modulation amplitude must be optimized. Thebinary approximation of the phase modulation results in the step-indexFresnel zone lens. The maximum efficiency of 90%, limited only bydiffraction, can be obtained in certain lenses.

[0200] Another type of optical waveguide device has been designed byspatially changing the K-vector as a function of distance to the centralaxis, using a so-called chirped Bragg grating configuration. In chirpedBragg grating configurations, the cross sectional areas of the region ofchangeable propagation constant 190 are thicker near the center of thewaveguide than the periphery to provide a greater propagation constantas shown in the embodiment of FIG. 30. Additionally, the output of eachregion of changeable propagation constant 190 is angled towards thefocal point to enhance the deflection of the light toward the deflectionpoint. The architecture of the FIG. 32 embodiment of chirped Bragggrating waveguide lens results in index modulation according to theequation:

Δn(x)=Δn cos[Δφ(x)]=Δn cos{Kn _(e) [Kn _(e)(ƒ−{square root}x ²+ƒ²)]}  16

[0201] Where ƒ=focal length, Δφ=phase difference; L is the lensthickness of the Bragg grating; x is the identifier of the grating line,and n is the refractive index. As required by any device based ongrating deflection, the Q parameter needs to be greater than 10 to reachthe Bragg region in order to have high efficiency. The grating linesneed to be gradiently slanted following the expression:

Ψ(x)=½ tan⁻¹(xƒ)≅x/2ƒ  17

[0202] so that the Bragg condition is satisfied over the entireaperture. The condition for maximum efficiency is:

kL=πΔnL/80 =π/2  18

[0203] In the embodiment of the optical waveguide device as configuredin FIG. 32, adjustments may be made to the path length of the lightpassing through the waveguide by using a gate electrode formed withcompensating prism shapes. Such compensating prism shapes are configuredso that the voltage taken across the gate electrode (from the side ofthe gate electrode adjacent the first body contact electrode to the sideof the gate electrode adjacent the second body contact electrode)varies. Since the voltage varies across the gate electrode vary, theregions of changeable propagation constant will similarly vary acrossthe width of the waveguide. Such variation in the voltage will likelyresult in a greater propagation of the light passing through thewaveguide at different locations across the width of the waveguide.

[0204]FIG. 33 shows a front view of another embodiment of opticalwaveguide device from that shown in FIG. 1. The optical waveguide device100 shown in FIG. 33 is configured to operate as a lens 3300. The depthof the electrical insulator layer 3302 varies from a maximum depthadjacent the periphery of the waveguide to a minimum depth adjacent thecenter of the waveguide. Due to this configuration, a greater resistanceis provided by the electrical insulator 3302 to those portions that areadjacent the periphery of the waveguide and those portions that are thecenter of the waveguide. The FIG. 33 embodiment of optical lens canestablish a propagation constant gradient across the width of thewaveguide. The value of the propagation constant will be greatest at thecenter, and lesser at the periphery of the waveguide. This embodiment oflens 3300 may utilize a substantially rectangular gate electrode. It mayalso be necessary to provide one or more wedge shape spacers 3306 thatare made from material having a lower electrical resistance than theelectrical insulator 3302 to provide a planer support surface to supportthe gate electrode. Other similar configurations in which the electricalresistance of the electrical insulator is varied to provide a variedelectrical field at the insulator/semiconductor interface and a variedpropagation constant level.

[0205] 3E. Optical Filters

[0206] The optical waveguide device 100 can also be modified to providea variety of optical filter functions. Different embodiments of opticalfilters that are described herein include an arrayed waveguide (AWG)component that acts as a multiplexer/demultiplexer or linear phasefilter in which a light signal can be filtered into distinct bandwidthsof light. Two other embodiments of optical filters are afinite-impulse-response (FIR) filter and an infinite-impulse-response(IIR) filter. These embodiments of filters, as may be configured withthe optical waveguide device, are now described.

[0207]FIG. 34 shows one embodiment of an optical waveguide device beingconfigured as an AWG component 3400. The AWG component 3400 may beconfigured to act as a wavelength multiplexer, wavelength demultiplexer,a linear phase filter, or a router. The AWG component 3400 is formed ona substrate 3401 with a plurality of optical waveguide devices. The AWGcomponent 3400 also includes an input waveguide 3402 (that may be formedfrom one waveguide or an array of waveguides for more than one inputsignal), an input slab coupler 3404, a plurality of arrayed waveguidedevices 3410, an output slab coupler 3406, and an output waveguide array3408. The input waveguide 3402 and the output waveguide array 3408 eachcomprise one or more channel waveguides (as shown in the FIGS. 1 to 3,4, or 5 embodiments) that are each optically coupled to the input slabcoupler 3402. Slab couplers 3404 and 3406 allow the dispersion of light,and each slab coupler 3404 and 3406 may also be configured as in theFIGS. 1 to 3 or 5 embodiments. Each one of the array waveguides 3410 maybe configured as in the FIGS. 10 to 11 embodiment of channel waveguide.Controller 201 applies a variable DC voltage V_(g) to some or all of thewaveguide couplers 3402, 3404, 3406, 3408, and 3410 to adjust forvariations in temperature, device age and characteristics, or otherparameters as discussed above in connection with the FIGS. 7-8. In theembodiment shown, controller 201 does not have to apply an alternatingcurrent signal V_(g) to devices 3402, 3404, 3406, 3408, and 3410.

[0208] The input array 3402 and the input slab coupler 3404 interact todirect light flowing through one or more of the input waveguides of thechannel waveguides 3410 depending upon the wavelength of the light. Eacharray waveguide 3410 is a different length, and can be individuallymodulated in a manner similar to described above. For example, the upperarray waveguides, shown with the greater curvature, have a greater lightpath distance than the lower array waveguides 3410 with lessercurvature. The distance that light travels through each of the arraywaveguides 3410 differs so that the distance of light exiting thedifferent array waveguides, and the resultant phase of the light exitingfrom the different array waveguides, differ.

[0209] Optical signals pass through the plurality of waveguides (of thechannel and slab variety) that form the AWG component 3400. The AWGcomponent 3400 is often used as an optical wavelength divisiondemultiplexer/multiplexer. When the AWG component 3400 acts as anoptical wavelength division demultiplexer, one input multi-bandwidthsignal formed from a plurality of input component wavelength signals ofdifferent wavelengths is separated by the AWG component 3400 into itscomponent plurality of output single-bandwidth signals. The inputmulti-bandwidth signal is applied to the input waveguide 3402 and theplurality of output single-bandwidth signals exit from the outputwaveguide array 3408. The AWG component 3400 can also operate as amultiplexer by applying a plurality of input single-bandwidth signals tothe output waveguide array 3408 and a single output multi-bandwidthsignal exits from the input waveguide 3402.

[0210] When the AWG component 3400 is configured as a demultiplexer, theinput slab coupler 3404 divides optical power of the inputmulti-bandwidth signal received over the input waveguide 3402 into aplurality of array signals. In one embodiment, each array signal isidentical to each other array signal, and each array signal has similarsignal characteristics and shape, but lower power, as the inputmulti-bandwidth signal. Each array signal is applied to one of theplurality of arrayed waveguide devices 3410. Each one of the pluralityof arrayed waveguide devices 3410 is coupled to the output terminal ofthe input slab coupler 3404. The AWG optical wavelength demultiplexeralso includes the output slab coupler 3406 coupled to the outputterminal of the plurality of arrayed waveguide devices 3410. Eacharrayed waveguide device 3410 is adapted to guide optical signalsreceived from the input slab coupler 3404 so each one of the pluralityof arrayed waveguide signals within each of the respective plurality ofarrayed waveguide devices (that is about to exit to the output slabcoupler) has a consistent phase shift relative to its neighboringarrayed waveguides device 3410. The output slab coupler 3406 separatesthe wavelengths of each one of the arrayed waveguide signals output fromthe plurality of arrayed waveguide devices 3410 to obtain a flatspectral response.

[0211] Optical signals received in at least one input waveguide 3402pass through the input slab coupler 3404 and then enter the plurality ofarrayed waveguide devices 3410 having a plurality of waveguides withdifferent lengths. The optical signals emerging from the plurality ofarrayed waveguide devices 3410 have different phases, respectively. Theoptical signals of different phases are then incident to the output slabcoupler 3406 in which a reinforcement and interference occurs for theoptical signals. As a result, the optical signals are focused at one ofthe output waveguide array 3408. The resultant image is then outputtedfrom the associated output waveguide array 3408.

[0212] AWG optical wavelength demultiplexers are implemented by anarrayed waveguide grating configured to vary its wavefront directiondepending on a variation in the wavelength of light. In such AWG opticalwavelength demultiplexers, a linear dispersion indicative of a variationin the shift of the main peak of an interference pattern on a focalplane (or image plane) depending on a variation in wavelength can beexpressed as follows: $\begin{matrix}{\frac{_{x}}{\lambda} = \frac{f\quad m}{n_{s}d}} & 19\end{matrix}$

[0213] where “f” represents the focal distance of a slab waveguide, “m”represents the order of diffraction, “d” represents the pitch of one ofthe plurality of arrayed waveguide devices 3410, and “n_(s)” is theeffective refractive index of the slab waveguide. In accordance withequation 19, the wavelength distribution of an optical signal incidentto the AWG optical wavelength demultiplexer is spatially focused on theimage plane of the output slab coupler 3406. Accordingly, where aplurality of output waveguides in array 3408 are coupled to the imageplane while being spaced apart from one another by a predetermineddistance, it is possible to implement an AWG optical wavelengthdemultiplexer having a wavelength spacing determined by the location ofthe output waveguide array 3408.

[0214] Optical signals respectively outputted from the arrayedwaveguides of the AWG component 3400 while having different phases aresubjected to a Fraunhofer diffraction while passing through the outputslab coupler 3406. Accordingly, an interference pattern is formed on theimage plane corresponding to the spectrum produced by the plurality ofoutput single-bandwidth signals. The Fraunhofer diffraction relates theinput optical signals to the diffraction pattern as a Fourier transform.Accordingly, if one of the input multi-bandwidth signals is known, it isthen possible to calculate the amplitude and phase of the remaininginput multi-bandwidth signals using Fourier transforms.

[0215] It is possible to provide phase and/or spatial filters thatfilter the output single-bandwidth signals that exit from the outputwaveguide array 3408. U.S. Pat. No. 6,122,419 issued on Sep. 19, 2000 toKurokawa et al. (incorporated herein by reference) describes differentversions of such filtering techniques.

[0216]FIG. 35 shows one embodiment of a finite-impulse-response (FIR)filter 3500. The FIR filter 3500 is characterized by an output that in alinear combination of present and past values of inputs. In FIG. 35,x(n) shows the present value of the input, and x(n−1), x(n−2), etc.represent the respective previous values of the input; y(x) representsthe present value of the output; and h(1), h(2) represent the filtercoefficients of x(n), y(n−1), etc. The D corresponds to the delay. TheFIR filter 3500 satisfies equation 20: $\begin{matrix}{y = {\sum\limits_{k = 0}^{M}{{h(k)}{x\left( {n - k} \right)}}}} & 20\end{matrix}$

[0217] An AWG, for example, is one embodiment of FIR filter in which thepresent output is a function entirely of past input. One combination ofoptical waveguide devices, a top view of which is shown in FIG. 36, is aFIR filter 3600 known as a coupled waveguide 3600. The coupled waveguide3600, in its most basic form, includes a first waveguide 3602, a secondwaveguide 3604, a coupling 3606, and a light pass grating 3608. Thefirst waveguide 3602 includes a first input 3610 and a first output3612. The time necessary of light to travel through the first waveguide3602 and/or the second waveguide 3604 corresponds to the delay D shownin the FIG. 35 model of FIR circuit. The second waveguide 3604 includesa second input 3614 and a second output 3616.

[0218] The coupling 3606 allows a portion of the signal strength of thelight flowing through the first waveguide 3602 to pass into the secondwaveguide 3604, and vice versa. The amount of light flowing between thefirst waveguide 3602 and the second waveguide 3604 via the coupling 3606corresponds to the filter coefficients h(k) in equation 20. Oneembodiment of light pass grating 3608 is configured as a Bragg gratingas shown in FIGS. 20 to 22. Controller 201 varies the gate voltage ofthe light pass grating to control the amount of light that passesbetween the first waveguide 3602 and the second waveguide 3604, andcompensates for variations in device temperature. An additional coupling3606 and light pass grating 3608 can be located between each additionalpair of waveguides that have a coefficient as per equation 20.

[0219]FIG. 37 shows one embodiment of a timing model of aninfinite-impulse-response (IIR) filter 3700. The FIG. 37 model of IIRfilter is characterized by an output that is a linear combination of thepresent value of the input and past values of the output. The IIR filtersatisfies equation 21: $\begin{matrix}{{y(n)} = {{x(n)} + {\sum\limits_{k = 1}^{M}{\alpha_{k}{y\left( {n - k} \right)}}}}} & 21\end{matrix}$

[0220] Where x(n) is a present value of the filter input; y(n) is thepresent value of the filter output; y(n−1), etc. are past values of thefilter output; and α₁, . . . , α_(M) are the filter coefficients.

[0221] One embodiment of an IIR filter 3800 is shown in FIG. 38. The IIRfilter 3800 includes an input waveguide 3801, a combiner 3802, awaveguide 3803, an optical waveguide device 3804, a waveguide 3805, abeam splitter 3806, an output waveguide 3807, and a delay/coefficientportion 3808. The delay/coefficient portion 3808 includes a waveguide3809, a variable optical attenuator (VOA) 3810, and waveguide 3812. Thedelay/coefficient portion 3808 is configured to provide a prescribedtime delay to the optical signals passing from the beam splitter 3806 tothe combiner 3802. In the FIG. 38 embodiment of an IIR filter 3800, Thetime necessary for light to travel around a loop defined by elements3802, 3803, 3804, 3805, 3806, 3809, 3810, and 3812 once equals the delayD shown in the FIG. 37 model of IIR circuit. The variable opticalattenuator 3810 is configured to provide a prescribed amount of signalattenuation to correspond to the desired coefficient, α₁ to α_(M). Anexemplary VOA is described in connection with FIG. 41 below.

[0222] Input waveguide 3801 may be configured, for example, as thechannel waveguide shown in FIGS. 1 to 3, 4, or 5. Combiner 3802 may beconfigured, for example, as a Bragg grating shown in FIGS. 20 to 22integrated in a slab waveguide shown in the FIGS. 1 to 3, 4, or 5. Thewaveguide 3803 may be configured, for example, as the channel waveguideshown in FIGS. 1 to 3, 4, or 5. The optical waveguide device 3804 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5. The waveguide 3805 may be configured, for example, as thechannel waveguide shown in FIGS. 1 to 3, 4, or 5. The beam splitter 3806may be configured, for example, as the beamsplitter shown below in FIG.46. The waveguide 3809 may be configured, for example, as the channelwaveguide shown in FIGS. 1 to 3, 4, or 5. The VOA 3810 may be configuredas shown below relative to FIG. 41. The waveguide 3812 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5.

[0223] Controller 201 applies a variable DC voltage V_(g) to therespective gate electrodes of the input waveguide 3801, the combiner3802, the waveguide 3803, the optical waveguide device 3804, thewaveguide 3805, the beam splitter 3806, the waveguide 3809, the VOA3810, and the waveguide 3812 to adjust for variations in temperature,device age, device characteristics, etc. as discussed below inconnection with FIGS. 7-8. In addition, controller 201 also varies thegate voltage applied to other components of the IIR to vary theiroperation, as discussed below.

[0224] During operation, an optical signal is input into the waveguide3801. Virtually the entire signal strength of the input optical signalflows through the combiner 3802. The combiner 3802 is angled to asufficient degree, and voltage is applied to a sufficient amount so thepropagation constant of the waveguide is sufficiently low to allow thelight from the waveguide 3801 to pass directly through the combiner 3802to the waveguide 3803. The majority of the light that passes intowaveguide 3803 continues to the optical waveguide device 3804. Theoptical waveguide device 3804 can perform a variety of functions uponthe light, including attenuation and/or modulation. For example, if itis desired to input digital signals, the optical waveguide device 3804can be pulsed on and off as desired when light is not transmitted to theoutput waveguide 3807 by varying the gate voltage of waveguide device3804. If the optical waveguide device 3804 is turned off and is fullyattenuating, then a digital null signal will be transmitted to theoutput waveguide 3807.

[0225] The output signal from the output waveguide device 3804 continuesthrough waveguide 3805 into beam splitter 3806. Beam splitter 3806diverts a prescribed amount of the light into waveguide 3809, and alsoallows prescribed amount of the light to continue onto the outputwaveguide 3807. The voltage applied to the gate of the beam splitter3806 can be changed by controller 201 to control the strength of lightthat is diverted to waveguide 3809 compared to that that is allowed topass to output waveguide 3807.

[0226] The light that is diverted through waveguide 3809 continuesthrough the variable optical attenuator 3810. The voltage applied to thevariable optical attenuator (VOA) 3810 can be adjusted depending uponthe desired coefficient. For example, fall voltage applied to the gateelectrode of the VOA 3810 would fully attenuate the light passingthrough the waveguide. By comparison, reducing the voltage applied tothe gate electrode would allow light to pass through the VOA to thewaveguide 3812. Increasing the amount of light passing through the VOAacts to increase the coefficient for the IIR filter corresponding to thedelay/coefficient portion 3808. The light that passes through to thewaveguide 3812 continues on to the combiner 3802, while it is almostfully deflected into waveguide 3803 to join the light that is presentlyinput from the input waveguide 3801 through the combiner 3802 to thewaveguide 3803. However, the light being injected from waveguide 3812into the combiner 3803 is delayed from the light entering from the inputwaveguide 3801. A series of these IIR filters 3800 can be arrangedserially along a waveguide path.

[0227]FIGS. 39 and 40 show two embodiments of a dynamic gain equalizerthat acts as a gain flattening filter. The structure and filteringoperation of the dynamic gain equalizer is described below.

[0228] 3F. Variable Optical Attenuators

[0229] A variable optical attenuator (VOA) is used to controllableattenuate one or more bandwidths of light. The VOA is embodiment ofoptical amplitude modulators, since optical attenuation may beconsidered a form of amplitude modulation. FIG. 41 shows one embodimentof a VOA 4100 that is modified from the FIGS. 1 to 3 or 5 embodiment ofoptical waveguide modulators. The VOA 4100 includes multiple sets ofpatterned Bragg gratings 4102 a, 4102 b, and 4102 c, multiple gateelectrodes 4104 a, 4104 b, and 4104 c, multiple variable voltage sources4106 a, 4106 b, and 4106 c, and a monitor 4108. Each individual plane inthe patterned Bragg gratings 4102 a, 4102 b, and 4102 c are continuouseven through they are depicted using dotted lines (since they arelocated behind, or on the backside of, the respective gate electrodes4104 a, 4104 b, and 4104 c).

[0230] Each of the multiple sets of patterned Bragg gratings 4102 a,4102 b, and 4102 c correspond, for example, to the embodiments of Bragggrating shown in FIGS. 20-22, and may be formed in the electricalinsulator layer or each respective gate electrode. The respective gateelectrode 4104 a, 4104 b, or 4104 c, or some insulative pattern isprovided as shown in the FIGS. 20 to 22 embodiments of Bragg gratings.In any one of the individual patterned Bragg gratings 4102 a, 4102 b,and 4102 c, the spacing between adjacent individual gratings is equal.However, the spacing between individual adjacent gratings the FIG. 41embodiment of patterned Bragg gratings 4102 a, 4102 b, and 4102cdecreases from the light input side to light output side (left toright). Since the grating size for subsequent patterned Bragg gratings4102 a, 4102 b, and 4102 c decreases, the wavelength of light refractedby each also decreases from input to output.

[0231] Each patterned Bragg gratings 4102 a-4102 c has a variablevoltage source applied between its respective gate electrode 4104 a,4104 b, and 4104 c and its common voltage first body contactelectrode/second body contact electrode. As more voltage is appliedbetween each of the variable voltage sources 4106 a, 4106 b, and 4106 cand the Bragg gratings 4102 a to 4102 c, the propagation constant ofthat patterned Bragg grating increases. Consequently, more light of therespective wavelengths λ₁, λ₂, or λ₃ associated with the spacing of thatpatterned Bragg gratings 4102 a to 4102 c would be refracted, andinterfere constructively. The monitor 4108 can monitor such light thatinterferes constructively.

[0232] Depending upon the intensity of the refracted light at eachwavelength, equation 22 applies.

P _(R)(λ₁)+P _(T)(λ₁)=P ₀(λ₁)  22

[0233] where P_(R)(λ₁) equals the refracted light, P_(T)(λ₁) equals thetransmitted light, and P₀(λ₁) equals the output light. In a typicalembodiment, a variable optical attenuator 4100 may be arranged with,e.g., 50 combined patterned Bragg gratings and gate electrodes (thoughonly three are shown in FIG. 41). As such, light having 50 individualbandwidths could be attenuated from a single light beam using thevariable optical attenuator 4100.

[0234] 3G. Programmable Delay Generators and Optical Resonators

[0235] Programmable delay generators are optical devices that add aprescribed, and typically controllable, amount of delay to an opticalsignal. Programmable delay generators are used in such devices asinterferometers, polarization control, and optical interferencetopography that is a technology used to examine eyes. In all of thesetechnologies, at least one optical signal is delayed. FIG. 42 shows atop view of one embodiment of a programmable delay generator 4200. FIG.43 shows a side cross sectional view of the FIG. 42 embodiment ofprogrammable delay generator 4200. In addition to the standardcomponents of the optical waveguide device shown in the embodiments ofFIGS. 1-3, 4, or 5, the programmable delay generator 4200 includes aplurality of Bragg grating devices 4202 a to 4202 e and a plurality ofaxially arranged gate electrodes 120. The embodiment of Bragg gratingsdevices 4202 shown in FIGS. 42 and 43 are formed in the lower surface ofthe gate electrode, however, the Bragg grating devices may alternativelybe formed as shown in the embodiments in FIGS. 20 to 22 as grooves inthe lower surface of the electrical insulator, as insulator elementshaving different resistance inserted in the insulator, as grooves formedin the lower surface of the gate electrode, or as some equivalent Braggstructure such as using surface acoustic waves that, as with the otherBragg gratings, project a series of parallel planes 4204, representingregions of changeable propagation constant, into the waveguide. Thespacing between the individual grooves in the Bragg grating equals somemultiple of the wavelength of light that to be reflected.

[0236] Each axially arranged gate electrode 120 is axially spaced ashort distance from the adjacent gate electrodes, and the spacingdepends upon the amount by which the time delay of light being reflectedwithin the programmable delay generator 4200 can be adjusted. Duringoperation, a gate voltage is applied to one of the axially arranged gateelectrodes 120 sufficient to increase the strength of the correspondingregion of changeable propagation constant sufficiently to reflect thelight travelling within the optical waveguide device.

[0237] As shown in FIG. 43, the gate electrode from Bragg grating device4202 c is energized, so incident light path 4302 will reflect off theregion of changeable propagation constant 190 associated with that gateelectrode and return along return light path 4304. The delay applied tolight travelling within the channel waveguide is therefore a function ofthe length of the channel waveguide between where light is coupled intoand/or removed from the channel waveguide and where the actuated gateelectrode projects its series of planes or regions of changeablepropagation constant. The light has to travel the length of the incidentpath and the return path, so the delay provided by the programmabledelay generator generally equals twice the incident path length dividedby the speed of light. By electronically controlling which of the Bragggrating devices 4202 a to 4202 e are actuated at any given time, thedelay introduced by the delay generator 4200 can be dynamically varied.

[0238] In one embodiment of operation for the programmable delaygenerator 4200, only one axially arranged gate electrode 120 isenergized with sufficient strength to reflect all the light since thatelectrode will reflect all of the light travelling within the waveguide.This embodiment provides a so-called hard reflection since one plane orregions of changeable propagation constant reflects all of the incidentlight to form the return light.

[0239] In another embodiment of operation for the programmable delaygenerator 4200, a plurality of adjacent, or axially spaced as desired,gate electrodes 120 are energized using some lesser gate voltage levelthan applied in the prior embodiment to reflect all of the light. Theplanes or regions of changeable propagation constant associated witheach actuated axially arranged gate electrode 120 each reflect somepercentage of the incident light to the return light path. The latterembodiment uses “soft” reflection since multiple planes or regions ofchangeable propagation constant reflect the incident light to form thereturn light.

[0240] Optical resonators are used to contain light within a chamber(e.g. the channel waveguide) by having the light reflect between opticalmirrors located at the end of that waveguide. The FIG. 44 embodiment ofresonator 4400 is configured as a channel waveguide so the light isconstrained within two orthogonal axes due to the total internalreflectance (TIR) of the channel waveguide. Light is also constrainedalong the third axis due to the positioning of TIR mirrors at eachlongitudinal end of the waveguide. The optical resonator 4400 forms atype of Fabry-Perot resonator. Resonators, also known as opticalcavities, can be integrated in such structures as lasers.

[0241] The resonator 4400 includes a optical waveguide of the channeltype, one or more input mirror gate electrodes 4402, one or more outputmirror gate electrodes 4404, and controllable voltage sources 4406 and4408 that apply voltages to the input mirror gate electrodes 4402 andthe output mirror gate electrodes 4404, respectively. FIG. 45 shows atop view of the channel waveguide of the resonator 4400 of FIG. 44. Thechannel waveguide includes, when the voltage sources 4406 and/or 4408are actuated, an alternating series of high propagation constant bands4502 and low propagation constant bands 4504.

[0242] The high propagation constant bands 4502 correspond to thelocation of the input mirror gate electrodes 4402 or the output mirrorgate electrodes 4404. The low propagation constant bands 4504 correspondto the bands between the input mirror gate electrodes 4402 or the outputmirror gate electrodes 4404. The high propagation constant bands 4502and the low propagation constant bands 4504 extend vertically throughthe waveguide. The input mirror gate electrodes 4402 and the outputmirror gate electrodes 4404 can be shaped to provide, e.g., a concavemirror surface if desired. Additionally, deactuation of the input mirrorgate electrodes 4402 or the output mirror gate electrodes 4404 removesany effect of the high propagation constant bands 4502 and lowpropagation constant bands 4504 from the waveguide of the resonator4400; Such effects are removed since the propagation constant approachesa uniform level corresponding to 0 volts applied to the gate electrodes4502, 4504.

[0243] As light travels axially within the waveguide of the resonator4400, some percentage of the light will reflect off any one of one ormore junctions 4510 between each high propagation constant band 4502 andthe adjacent low propagation constant band 4504, due to the reducedpropagation constant. Reflection off the junctions 4510 between highindex areas and low index areas forms the basis for much of thin filmoptical technology. The junction 4510 between each high propagationconstant band 4502 and the adjacent low propagation constant band 4504can be considered analogous to Bragg gratings. The greater the numberof, and the greater the strength of, such junctions 4510, the more lightthat will be reflected from the respective input mirror gate electrodes4402 or the output mirror gate electrodes 4404. Additionally, thegreater the voltage applied from the controllable voltage sources 4406and 4408 to the respective input mirror gate electrodes 4402 or theoutput mirror gate electrodes 4404, the greater the difference inpropagation constant between the high propagation constant band 4502 andthe adjacent low propagation constant band 4504 for the respective inputmirror gate electrodes 4402 or the output mirror gate electrodes 4404.

[0244]FIG. 46 shows a top view of one embodiment of beamsplitter 4600that is formed by modifying the optical waveguide device 100 shown inFIG. 46. The beamsplitter includes an input mirror 4602 having a firstface 4604 and a second face 4606. The mirror 4602 may be established inthe waveguide in a similar manner to a single raised land to provide avaried electrical field at the insulator/semiconductor interface in oneof the embodiments of Bragg gratings shown in FIGS. 20 to 22. Thevoltage level applied to the gate electrode 120 is sufficient toestablish a relative propagation constant level in the region ofchangeable propagation constant to reflect a desired percentage of lightfollowing incident path 101 to follow path 4610. The region ofchangeable propagation constant takes the form of the mirror 4602. Lightfollowing incident path 101 that is not reflected along path 4610continues through the mirror 4602 to follow the path 4612. Such mirrors4602 also reflect a certain percentage of return light from path 4612 tofollow either paths 4614 or 101. Return light on path 4610 thatencounters mirror 4602 will either follow path 101 or 4614. Return lighton path 4614 that encounters mirror 4602 will either follow path 4612 orpath 4610. The strength of the voltage applied to the gate electrode 120and the resulting propagation constant level of the region of changeablepropagation constant in the waveguide, in addition to the shape and sizeof the mirror 4602 determine the percentage of light that is reflectedby the mirror along the different paths 101, 4610, 4612, and 4614.

[0245] 3H. Optical Application Specific Integrated Circuits (OASICS)

[0246] Slight modifications to the optical functions and devices such asdescribed in FIGS. 16 to 25, taken in combination with free-carrierbased active optics, can lead to profound changes in optical designtechniques. Such modifications may only involve minor changes to thestructure of the gate electrode.

[0247] The optical waveguide device may be configured as a variableoptical attenuator that changes voltage between the gate electrode, thefirst body contact electrode, and the second body contact electrode,such that a variable voltage is produced across the width of thewaveguide. This configuration results in a variable attenuation of thelight flowing through the waveguide across the width of the waveguide.

[0248] If a magnetic field is applied to the 2DEG, then thefree-carriers exhibit birefringence. The degree of birefringence dependson the magnitude of the magnetic field, the free-carrier or 2DEGdensity, and the direction of propagation of the optical field relativeto the magnetic field. The magnetic field may be generated bytarditional means, i.e. from passing of current or from a permanentmagnet. The magnetic field induced birefringence can be harnessed tomake various optical components including polarization retarders, modecouplers, and isolators.

[0249] IV. Integrated Optical Circuits including Optical WaveguideDevices

[0250] 4A. Introduction to Integrated Optical Circuits

[0251] The optical functions of the optical waveguide devices describedabove can be incorporated onto one (or more) chip(s) in much the sameway as one currently designs application specific integrated circuits(ASICS) and other specialized electronics, e.g., using standardlibraries and spice files from a foundry. The optical functions of theoptical waveguide devices described herein can be synthesized anddesigned in much the same way as electronic functions are, using ASICS.One may use an arithmetic logic unit (ALU) in a similar manner thatASICS are fabricated. This level of abstraction allowed in the design ofoptical circuits by the use of optical waveguide devices improves thecapability of circuit designers to create and fabricate such large scaleand innovative designs as have been responsible for many of thesemiconductor improvements in the past.

[0252] Ad discussed above, different devices can be constructed bymodifying the basic structure described in FIG. 1 by, e.g. changing theshape, configuration, or thickness of the gate electrode. These modifieddevices can provide the building blocks for more complex circuits, in asimilar manner that semiconductor devices form the basic building blocksfor more complex integrated circuit structures.

[0253] The disclosure now describes a variety of integrated opticalcircuits that can be constructed using a plurality of optical waveguidedevices of the type described above. The integrated optical circuitsdescribed are illustrative in nature, and not intended to be limiting inscope. Following this description, it becomes evident that the majorityof functions that are presently performed by using current integratedcircuits can also be formed using integrated optical circuits. Theadvantages are potential improvement in operating circuit capability,cost, and power consumption. It is to be understood that certain ones ofthe functions shown as being performed by an active optical waveguidedevice in the following integrated optical circuits may also beperformed using a passive device. For example, devices 4708 and 4712 inthe embodiment shown in FIG. 47 may be performed by either activedevices or passive devices. The embodiment of beamsplitter 4600 shown inFIG. 46 can either be an active or passive device. The selection ofwhether to use an active or passive device depends, e.g., on theoperation of the integrated optical circuit with respect to eachparticular optical waveguide device, and the availability of eachoptical waveguide device in active or passive forms.

[0254] It is emphasized that the multiple optical waveguide devices ofthe types described above relative to FIGS. 1-3, 4, or 5 may be combinedin different ways to form the following described integrated opticalcircuits shown, for example, in the embodiments of FIGS. 18, 19, 34, 36,38-45, and 47-49. For example, the different integrated optical circuitembodiments may be formed using a plurality of optical waveguide devicesformed on a single substrate. More particularly, the differentembodiments of integrated optical circuits may comprise multiple opticalwaveguide devices attached to different portions of a single waveguide.Alternatively, the different embodiments of integrated optical circuitsincluding multiple optical waveguide devices may be formed on aplurality of discrete optical waveguide devices.

[0255] 4B. Dynamic Gain Equalizer

[0256]FIG. 39 shows one embodiment of a dynamic gain equalizer 3900comprising a plurality of optical waveguide devices. The dynamic gainequalizer 3900 comprises a wavelength separator 3902 (that may be, e.g.an arrayed waveguide or an Echelle grating), a beam splitter 3904, amonitor 3906, the controller 201, a variable optical attenuator bank3910, a wave length combiner 3912, and an amplifier 3914. Dynamic gainequalizers are commonly used to equalize the strength of each one of aplurality of signals that is being transmitted over relatively longdistances. For example, dynamic gain equalizers are commonly used inlong distance optical telephone cables and a considerable portion of thesignal strength is attenuated due to the long transmission distancesbetween, e.g., states or countries.

[0257] The wavelength separator 3902 acts to filter or modulate thewavelength of an incoming signal over waveguide 3916 into a plurality oflight signals. Each of these light signals has a different frequency.Each of a plurality of waveguides 3918 a to 3918 d contain a lightsignal of different wavelength λ₁ to λ_(n), the wavelength of eachsignal corresponds to a prescribed limited bandwidth. For example,waveguide 3918 a carries light having a color corresponding towavelength λ₁, while waveguide 3918 carries a light having a colorcorresponding to wavelength λ₂, etc.

[0258] Each of the waveguides 3918 a to 3918 d is input into the beamsplitter 3904. The beam splitter outputs a portion of its light into avariable optical attenuator 3910, and also deflects a portion of itslight to the monitor 3906. The monitor 3906 senses the proportionalsignal strength that is being carried over waveguide 3918 a to 3918 d.Both the monitor 3906 and the beam splitter 3904 may be constructedusing the techniques for the optical waveguide devices described above.The controller 201 receives a signal from the monitor that indicates thesignal strength of each monitored wavelength of light being carried overwaveguides 3918 a to 3918 d.

[0259] The controller monitors the ratios of the signal strengths of thedifferent wavelength bands of light carried by waveguides 3918 a to 3918d, and causes a corresponding change in the operation of the variableoptical attenuator bank 3910. The variable optical attenuator bank 3910includes a plurality of variable optical attenuators 3930 a, 3930 b,3930 c and 3930 d that are arranged in series. Each VOA selectivelyattenuates light that originally passed through one of the respectivewaveguides 3918 a to 3918 d. The number of variable optical attenuators3930 a to 3930 d in the variable optical attenuator bank 3910,corresponds to the number of light bands that are being monitored overthe waveguides 3918 a to 3918 d. If the signal strength of one certainlight band is stronger than another light band, e.g., assume that thelight signal travelling through waveguide 3918 a is stronger than thelight signal travelling through 3918 b, then the stronger opticalsignals will be attenuated by the desired attenuation level by thecorresponding attenuator. Such attenuation makes the strength of eachoptical signal substantially uniform.

[0260] As such, all of the signal strengths on the downstream side ofthe variable optical attenuators 3930 a, 3930 b, 3930 c and 3930 dshould be substantially equal, and are fed into a wavelength signalcombiner 3912, where all the signals are recombined into a singlesignal. The optical signal downstream of the wavelength combiner 3912,therefore, is gain equalized (and may be considered as gain flattened).The signal downstream of the wavelength combiner 3912 may still berelatively weak due to a faint original signal or the relativeattenuation of each wavelength by the variable optical attenuator.Therefore, the signal is input into the amplifier 3914. The amplifier,that is one embodiment is an Erbium Doped Fiber Amplifier (EDFA),amplifies the strength of the signal uniformly across the differentbandwidths (at least from λ₁ to λ_(n)) to a level where it can betransmitted to the next dynamic gain equalizer some distance down outputwaveguide 3932. Using this embodiment, optical signals can be modulatedwithout being converted into, and from, corresponding electricalsignals. The variable optical attenuators 3930 a to 3930 d and the wavelength combiner 3912 can be produced and operated using the techniquesdescribed above relating to the optical waveguide devices.

[0261]FIG. 40 shows another embodiment of a dynamic gain equalizer 4000.The beam splitter 4003 and the monitor 4006 are components in the FIG.40 embodiment of dynamic gain equalizer 4000 that are locateddifferently than in the FIG. 39 embodiment of dynamic gain equalizer3900. The beam splitter 4004 is located between the variable opticalattenuator (VOA) bank 3910 and the wavelength combiner 3912. Thewavelength combiner 3912 may be fashioned as an arrayed waveguide (AWG)as shown in the embodiment of FIG. 34 (in a wavelength multiplexingorientation). The beam splitter 4004 is preferably configured to reflecta relatively small amount of light from each of the respective VOAs 3930a, 3930 b, 3930 c, and 3930 d. The beam splitter 4004 is configured toreflect a prescribed percentage of the light it receives from each ofthe VOAs 3930 a to 3930 d to be transmitted to the monitor 4006. Themonitor 4006 converts the received light signals which relate to thestrength of the individual light outputs from the VOAs 3930 a to 3930 dinto a signal which is input to the controller 201. The controller 201,which preferably is configured as a digital computer, an applicationspecific integrated-circuit, or perhaps even an on chip controller,determines the strengths of the output signals from each of therespective VOAs 3930 a to 3930 d and balances the signal strengths byselective attenuation. For example, assume that the output signal of VOA23930 b is stronger than that of VOA 33930 c, as well as the rest of theVOAs. A signal attenuator would be actuated to attenuate the VOA 23930 bsignal appropriately. As such, the controller 201 selectively controlsthe attenuation levels of the individual VOAs 3930 a to 3930 d.

[0262] Each output light beam from VOAs 3930 a to 3930 d that continuesstraight through the beam splitter 4004 is received by the wavelengthcombiner 3912, and is combined into a light signal that contains all thedifferent wavelength signals from the combined VOAs 3930 a to 3930 d.The output of the wavelength 3912 is input into the amplifier, and theamplifier amplifies the signal uniformly to a level wherein it can betransmitted along a transmission waveguide to, for example, the nextdynamic gain equalizer 4000.

[0263] 4C. Self Aligning Modulator

[0264] The FIG. 47 embodiment of self-aligning modulator 4700 is anothersystem that performs an optical function that may include a plurality ofoptical waveguide devices. The self-aligning modulator 4700 includes aninput light coupler 4702, a first deflector 4704, a second deflector4706, an input two dimensional lens 4708 (shown as a Bragg grating typelens), a modulator 4710, an output two dimensional lens 4712 (shown as aBragg grating type lens), an output light coupler 4716, and thecontroller 201.

[0265] The input light coupler 4702 acts to receive input light that isto be modulated by the self-aligning modulator 4700, and may be providedby any type of optical coupler such as an optical prism. The firstdeflector 4704 and the second deflector 4706 are directed to operate inopposed lateral directions relative to the flow of light through theself-aligning modulator 4700. The input two dimensional lens 4708 actsto focus light that it receives from the deflectors 4704 and 4706 so thelight can be directed at the modulator 4710. The modulator 4710modulates light in the same manner as described above. The modulator maybe formed as one of the optical waveguide devices shown in FIGS. 1-3, 4,and 5. The deflected light applied to the modulator 4710 is both alignedwith the modulator and focused. The output two-dimensional lens 4712receives light output from the modulator 4710, and focuses the lightinto a substantially parallel path so that non-dispersed light can bedirected to the output prism 4716. The output light coupler 4716receives light from the output two-dimensional lens 4712, and transfersthe light to the outside of the self-aligning modulator 4700. Thecontroller 201 may be, e.g., a microprocessor formed on a substrate4720. The controller 201 controls the operation of all the activeoptical waveguide devices 4704, 4706, 4708, 4710, and 4712 included onthe self-aligning modulator 4700.

[0266] While the modulator 4710 and the two-dimensional lenses 4008,4012 are shown as active optical waveguide devices, it is envisionedthat one or more passive devices may be substituted while remainingwithin the scope of the present invention. The two-dimensional lenses4008, 4012 are optional, and the self-aligning modulator will operatewith one or none of these lenses. During operation, the first deflector4704 and the second deflector 4706 are adjusted to get the maximumoutput light strength through the output prism 4716.

[0267] The self-aligning modulator 4700 ensures that a maximum, orspecified level, amount of light applied to the input prism 4702 ismodulated by the modulator 4710 and released to the output prism 4716.The performance of the self-aligning modulator system 4700 can also bechecked simultaneously. For instance, if light exiting from the outputprism is reduced, the deflectors, the lenses, and the monitor may eachbe individually varied to determine whether it causes any improvement inoperation. Other suitable control techniques and algorithms may be usedto derive an optimal operation. FIGS. 47, 48, and 49 further demonstratehow a variety of optical waveguide devices may be located on a singlesubstrate or chip.

[0268] One or more optical waveguide devices may be configured as amulti-function optical bench that facilitates alignments of a laser tothe fiber. In the optical bench configuration, that is structuredsimilarly to the FIG. 47 embodiment of the self-aligning modulator 4700,a plurality of the FIGS. 1 to 3, 4, or 5 embodiments of opticalwaveguide devices are integrated on the substrate. For example, awaveguide can be formed in the substrate so that only the gateelectrode, the first body contact electrode, the second body contactelectrode, and the electrical insulator layer have to be affixed to thesubstrate to form the FET portion. The corresponding FET portions areattached to the substrate (the substrate includes the waveguide). Assuch, it is very easy to produce a wide variety of optical waveguidedevices.

[0269] 4D. Optical Systems Using Delay Components

[0270]FIGS. 48 and 49 show several embodiments of systems that my beconstructed using one or more of the embodiments of programmable delaygenerator 4200 shown in FIGS. 42 and 43. FIGS. 48 shows one embodimentof a polarization controller. FIG. 49 shows one embodiment ofinterferometer.

[0271] Polarization control is a method used to limit interferencebetween a plurality of different polarizations that occur, for example,when light is transmitted in a fiber for a large distance such as 3,000kilometers or more. Light that is to be transmitted over the fiber isoften split into two polarizations, referred to as P polarization and Spolarization. The polarization is received at the other end of the fiberin some arbitrary polarization state since the fiber may encounterdifferent propagation constants for the P polarization signal and the Spolarization signal. Therefore, the P polarization signal and the Spolarization signal may be modulated within the fiber differently, andmay travel at different rates, and may be attenuated differently. Forexample, the duration between a first polarization and a secondpolarization may extend from a duration indicated as d to a longerduration shown as d′ as the signal is transmitted over a longtransmission fiber. When multiple data bits are transmitted, the Ppolarization signal and the S polarization signal for adjacent bits mayoverlap due to the different velocities of the polarizations. Forexample, one polarization of the previous bit is overlapping with theother polarization of the next bit. If a network exceeds a hundredpicoseconds at 10 gigahertz, there is a large potential for suchoverlap. An example of such a network is Network Simplement, nextgeneration network presently under development in France.

[0272] The embodiment of polarization controller 4800 shown in FIG. 48comprises a transmission fiber 4802, an output 4804, an adjustablepolarizer 4806, a beamsplitter 4808, a first path 4810, a second path4812, and a combiner 4813 that combines the first path and the secondpath. The first path 4810 includes a programmable delay generator 4814.The second path 4812 comprises a programmable delay generator 4816. Thetransmission fiber 4802 may be fashioned as a channel waveguide oroptical fiber. The adjustable polarizer 4806 may be fashioned as a slabwaveguide. The beamsplitter 4808 may be fashioned as the beamsplitter4600 shown and described relative to FIG. 46. The combiner 4813 may befashioned as the arrayed waveguide (AWG) shown and described relative toFIG. 34 configured as a multiplexer. The programmable delayed generators4814 and 4816 may be fashioned as the embodiment of programmable delaygenerator 4200 shown and described relative to FIG. 42.

[0273] During operation, light travelling down the transmission fiber4802 may be formed from a plurality of temporarily spaced data bits,with each data bit having a P polarization and an S polarization. Thetemporal separation between a first polarization and a secondpolarization may separate from a distance shown as d to a distance shownas d′. Approximately every couple thousand miles, or as determinedsuitable for that particular transmission system, one polarizationcontroller 4800 can be located within the transmission system to limitany adverse overlapping of polarizations.

[0274] The polarization controller 4800 acts to adjust the temporalspacing of each signal, and therefor limits the potential that the timebetween adjacent polarizations from adjacent signals is reduced to thepolarizations are in danger of overlapping. As such, as the opticalsignal is received at the output 4804 of the transmission fiber 4802, itencounters the polarizer 4806 that separates the polarized signals.After the polarized signals are cleanly separated, the signal continueson to the beamsplitter. The beamsplitter 4808 splits the signal into twopolarizations, such that a first polarization follows the first path4810 and the second polarization follows a second path 4812. Theprogrammable delay generators 4814 and 4816 are included respectively inthe first path 4810 and the second path 4812 to temporally space therespective first polarization (of the P or S variety) and the secondpolarization (of the opposed variety) by a desired and controllableperiod. Providing a temporal delay in the suitable programmable delaygenerator 4814, 4816 allows the controller 201 to adjust the temporalspacing between the P polarization and the S polarization by aprescribed time period, as dictated by the operating conditions of thenetwork. It is common in long data transmission system to have the Ppolarization and the S polarization temporally separate further apart.The polarization controller 4800 readjusts the time between the Spolarization and the P polarization. As such, the S polarization or theP polarization will not overlap with the polarizations from adjacentsignals.

[0275] For a given fiber, each color has its own polarization controller4800. There might be 80 colors being used in a typical optical fiber, sothere have to be a large number of distinct polarization controllers tohandle all the colors in a fiber. A central office for a telephonenetwork may be terminating a large number of fibers (e.g., 100). Assuch, a central office may need 8000 polarization controllers at acentral office to deal with the dispersion problem on all of theirfibers. As such, expense and effectiveness of operation of eachpolarization controller are important.

[0276]FIG. 50 shows one embodiment of a method 5000 that can performedby the controller 201 in maintaining the temporal separation of a firstpolarization and a second polarization between and input optical signaland an output optical system. The method 5000 starts with block 5002 inwhich the controller detects the first temporal separation of a firstpolarization and a second polarization in the output optical signal. Theoutput optical signal may be considered to be that signal which isapplied to the input 4804 in FIG. 48, as referenced by the character d′.

[0277] The method 5000 continues to block 5004 in which the controller201 compares the first temporal separation of the output optical signalto a second temporal separation of an input optical signal. The inputoptical signal is that signal which is initially applied to thetransmission fiber, and is indicated by the referenced character d inFIG. 48. The controller 201 typically stores, or can determine, thevalue of the second temporal separation between the first polarizationand the second polarization. For example, a transmitter, or transmissionsystem, that generates the signal using two polarizations may typicallyprovide a fixed delay d between all first polarizations and thecorresponding second polarizations in the input optical signal.Alternatively, the controller 201 may sense whether the temporalseparation distance d′ between first polarization and the secondpolarization of the output optical signal are becoming too far apart. Inboth cases it is desired to reduce the second temporal separation.

[0278] The method 5000 continues to step 5006 in which the controller201 separates the input optical signal into two paths, indicated as thefirst path 4810 and the second path 4812 in FIG. 48. The separated firstpolarization from the output optical signal is transmitted along thefirst path 4810. The separated second polarization from the outputoptical signal is transmitted along the second path 4812.

[0279] The method continues to step 5008 in which the controller, usingeither the first programmable delay generator 4814 or the secondprogrammable delay generator 4816 that are located respectively in thefirst path 4810 and the second path 4812, delay the light flowingthrough their respective paths. Such a delay of the light along eachrespective path 4810, 4812 corresponds to the respective firstpolarization or the second polarization travelling through eachrespective path. One embodiment of the delay of the light in therespective programmable delay generators 4814, 4816 is provided in asimilar matter to as described in the embodiments of programmable delaygenerator 4200 shown in FIGS. 42 and 43. The method 5000 continues toblock 5010 in which the first polarization that travels over the firstpath 4810 and the second polarization that travels over the second path4812 are combined (and include the respective delays for eachpolarization). Combining these signals form an output optical signalhaving its temporal spacing between the first polarization and thesecond polarization modified. This output optical signal having modifiedtemporal spacing may be input as an input optical signal to a new lengthof transmission fiber, or may be transmitted to the end user.

[0280]FIG. 49 shows one embodiment of an interferometer that may beconstructed using optical waveguide devices, including one or moreprogrammable delay generators 4200. The interferometer 4900 (e.g., aMichelson interferometer) comprises a laser 4902, a beamsplitter 4904, afirst programmable delay generator 4906, a second programmable delaygenerator 4908, and an interference detector 4910. In the interferometer4900, one or both of the first programmable delay generator 4906 and thesecond programmable delay generator 4908 must be provided. If only oneof the two programmable delay generators is provided, then a mirror issubstituted at the location of the missing programmable delay generator.

[0281] During operation, coherent light is applied from the laser 4902.The coherent light, follows path 4920 and encounters the beamsplitter4904. The beamsplitter splits the coherent light from the laser into tofollow either path 4922 or path 4924. Light following path 4922 willencounter the first programmable delay generator 4906 and will bereflected back toward the beamsplitter. Light following path 4924 willencounter the second programmable delay generator 4908 and will bereflected back toward the beamsplitter 4904. As a return path of lightfrom travelling along path 4924 and 4922 encounters the beamsplitter, acertain proportion of the return light following both paths 4924 and4922 will be reflected to follow path 4926.

[0282] Based upon the position of the first and second programmabledelay generators 4906, 4908, the light travelling along paths 4922 and4924 will travel a different distance (the distances traveled includethe original path and the return path from the programmable delaygenerator). These differences in distances will be indicated by theinterference pattern in the signal following path 4926. Depending on thewavelength of light used in the Michelson interferometer, the Michelsoninterferometer may be used to measure differences in distance betweenpath 4922 and 4924. In one embodiment, one or more of the programmabledelay generator shown as 4906, 4908 is replaced by a mirror or a likedevice. For example, a modified Michelson interferometer may be used asin optical interference topography in which the position of the retina,relative to the eye, is measured to determine the state of the eye. Theretina acts as a mirror, and focuses some of the light out of the eye.Therefore, an interferometer, or more specifically an opticalinterference topography device can detect light reflected off theretina. As such, in the Michelson interferometer, one of theprogrammable delay generators 4906 or 4908 can be replaced by the eye ofthe examined patient. The other one of the programmable delay generators4908, 4906 can be used to measure distances within the eye.

[0283] The embodiment of the methods shown in FIGS. 7 and 8 may be usedto adjust or calibrate the voltage applied to an electrode of an opticalwaveguide devices based on variations in such parameters as device ageand temperature. These methods rely on such inputs as the temperaturesensor 240 measuring the temperature of the optical waveguide device andthe meter 205 measuring the resistance of the gate electrode, as well asthe controller 201 controlling the operation of the optical waveguidedevice and controlling the methods performed by FIGS. 7 and 8. Themethods may be applied to systems including a large number of opticalwaveguide devices as well as to a single optical waveguide device. Assuch, the optical waveguide system, in general, is highly stable andhighly scalable.

[0284] While the principles of the invention have been described abovein connection with the specific apparatus and associated method, it isto be clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the invention.

What is claimed is:
 1. An optical filter that filters an input opticalsignal in order to generate a filtered output optical signal,comprising: a waveguide that includes an input port wherein the inputoptical signal is introduced into the waveguide, an output port whereinthe filtered output optical signal exits the waveguide, and a region offiltering propagation constant disposed along a length of the waveguideand between the input port and the output port, wherein the inputoptical signal is guided by total internal reflection in the waveguide,and the waveguide is formed at least in part from an activesemiconductor; a first electrode positioned proximate a first surface ofthe region of filtering propagation constant and electrically separatedfrom the active semiconductor; a second electrode in electrical contactwith the active semiconductor and disposed on a first side of the regionof filtering propagation constant; a two-dimensional electron (hole) gas(2DEG) having a free carrier distribution that is formed on the firstsurface of the active semiconductor when a voltage is applied betweenthe first electrode and the second electrode; and wherein changing thevoltage causes a corresponding change of the free carrier distributionwhich, in turn, causes corresponding change of a propagation constantlevel in the region of filtering propagation constant that filters theinput optical signal flowing through the region of filtering propagationconstant.
 2. The optical filter of claim 1, further comprising a thirdelectrode in electrical contact with the active semiconductor disposedon a second side of the region of filtering propagation constantopposite the first side; wherein the second and third electrodes areelectrically coupled to a common potential.
 3. The optical filter ofclaim 1 or 2, wherein the 2DEG is oriented in a plane that issubstantially parallel to said length.
 4. The optical filter of claim 2,further comprising a field effect transistor (FET) portion that includesthe first, second, and third electrodes.
 5. The optical filter of claim4, wherein the FET portion is from one of the group ofmetal-oxide-semiconductor FET (MOSFET), metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor field effecttransistor (MESFET), a high electron mobility transistor (HEMT), or amodulation doped FET (MODFET).
 6. The optical filter of claim 1, furthercomprising a metal oxide semiconductor capacitor (MOSCAP) portion. 7.The optical filter of claim 6, wherein the body contact electrode islocated below the waveguide.
 8. The optical filter of claim 1, whereinthe waveguide comprises any group III or group V semiconductor.
 9. Theoptical filter of claim 1, wherein the free-carrier distribution of the2DEG layer is varied by changing the voltage applied to the firstelectrode, and wherein light flowing through the waveguide iscontrollably attenuated in response to the voltage applied to the firstelectrode.
 10. The optical filter of claim 1 that includes aninfinite-impulse-response (IIR) filter characterized by an output thatis a linear combination of a present input value and past output values.11. The optical filter of claim 1 that includes anfinite-impulse-response (FIR) filter characterized by an output that isa linear combination of present and past input values.
 12. The opticalfilter of claim 1 that includes an arrayed waveguide.
 13. The opticalfilter of claim 1 that includes a frequency domain filter region.
 14. Anoptical filter having characteristics that vary in response to changesin a propagation constant level of a region of filtering propagationconstant of a waveguide, comprising: a gate electrode having aprescribed electrode shape positioned proximate the waveguide; a voltagesource that applies voltage to the gate electrode, wherein the voltagecauses the gate electrode to project into the waveguide the region offiltering propagation constant, said region of filtering propagationconstant corresponding generally in shape to the prescribed electrodeshape and filtering light flowing through the waveguide; and acontroller that controls the propagation constant level of the region offiltering propagation constant and the characteristics of the filter byvarying the voltage applied to the gate electrode to adjustably filterlight flowing through the waveguide.
 15. The optical filter of claim 14that includes an infinite-impulse-response (IIR) filter characterized byan output that is a linear combination of a present input value and pastoutput values.
 16. The optical filter of claim 14 that includes anfinite-impulse-response (FIR) filter, the FIR filter is characterized byan output that is a linear combination of the present and past values ofthe inputs.
 17. The optical filter of claim 14 that includes an arrayedwaveguide.
 18. The optical filter of claim 14 that includes a frequencydomain filter region.
 19. The optical filter of claim 14, furthercomprising a 2DEG oriented in a plane that is substantially parallel tothe region of filtering propagation constant.
 20. The optical filter ofclaim 14, further comprising a field effect transistor (FET) portionincluding a source electrode and a drain electrode.
 21. The opticalfilter of claim 14, wherein the FET is from one of the group ofmetal-oxide-semiconductor FET (MOSFET), metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor field effecttransistor (MESFET), a high electron mobility transistor (HEMT), or amodulation doped FET (MODFET).
 22. The optical filter of claim 14,further comprising one or more body contact electrode(s) positionedrelative to the waveguide and electrically integrated with an activesemiconductor.
 23. The optical filter of claim 14, further comprising ametal oxide semiconductor capacitor (MOSCAP) portion that includes thebody contact electrode.
 24. The optical filter of claim 14, wherein thebody contact electrode is located below the waveguide.
 25. The opticalfilter of claim 14, wherein the body contact electrode includes a firstbody contact electrode and a second body contact electrode, the firstbody contact electrode, the gate electrode, and the second body contactelectrode are located above the waveguide.
 26. The optical filter ofclaim 25, wherein the first body contact electrode is located on anopposed side of the gate electrode from the second body contactelectrode, and wherein the waveguide comprises any group III or group Vsemiconductor.
 27. The optical filter of claim 19, wherein thefree-carrier distribution of the 2DEG layer is varied by changing thevoltage applied to the gate electrode, and wherein light flowing throughthe waveguide is controllably attenuated in response to the voltageapplied to the gate electrode.
 28. The optical filter of claim 14,further comprising an optical device coupled with a variable coupling tothe optical filter.
 29. A method for varying the light filteringcharacteristics of an optical device by changing a propagation constantlevel of a region of filtering propagation constant of a waveguide inthe optical device, the method comprising: positioning a planarelectrode proximate the waveguide; applying a voltage to the planarelectrode to change the level of propagation constant in the region offiltering propagation constant in the waveguide wherein the region offiltering propagation constant corresponds in shape to a shape of theplanar electrode; and controlling a propagation constant level of theregion of filtering propagation constant and the filteringcharacteristics of the optical device by varying the voltage.
 30. Themethod of claim 29, further comprising a 2DEG located between the planarelectrode and a body contact electrode, wherein the 2DEG is oriented ina plane that is substantially parallel to a length of the region offiltering propagation constant.
 31. The method of claim 29, furthercomprising a field effect transistor (FET) portion including the planarelectrode.
 32. The method of claim 31, wherein the FET is from one ofthe group of metal-oxide-semiconductor FET (MOSFET), metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor field effecttransistor (MESFET), a high electron mobility transistor (HEMT), or amodulation doped FET (MODFET).
 33. The method of claim 29, furthercomprising one or more body contact electrode(s) positioned relative tothe waveguide and electrically integrated with an active semiconductor.34. The method of claim 29, further comprising a metal oxidesemiconductor capacitor (MOSCAP) portion including a body contactelectrode.
 35. The method of claim 34, wherein the body contactelectrode is positioned below the waveguide.
 36. The method of claim 34,wherein the body contact electrode includes a first body contactelectrode and a second body contact electrode, the first body contactelectrode, the planar electrode, and the second body contact electrodeare located above the waveguide; and the first body contact electrode islocated on an opposed side of the planar electrode from the second bodycontact electrode.
 37. The method of claim 29, wherein the waveguidecomprises any group III or group V semiconductor.
 38. The method ofclaim 30, wherein the free-carrier distribution of the 2DEG layer ischanged by changing the voltage applied to the planar electrode, andwherein light flowing through the waveguide is controllably changed inresponse to changing the free-carrier distribution of the 2DEG layer.39. The method of claim 29, further comprising an optical device coupledwith a variable coupling to the optical filter.
 40. A computer readablemedium containing software that controls a planar electrode having aprescribed shape positioned proximate a waveguide, said software whenexecuted by a processor causes the processor to perform the steps of:projecting a region of filtering propagation constant into the waveguidethat corresponds in shape to the prescribed shape, by applying a voltageto the electrode; and controlling a propagation constant level of theregion of filtering propagation constant and filtering characteristicsof the waveguide by varying the voltage.
 41. An optical filter havinglight filtering characteristics that vary with changes to a propagationconstant level of a waveguide, the optical filter comprising: a regionof filtering propagation constant disposed along a length of thewaveguide and defining a region where light is filtered, wherein thelight is guided within the waveguide by total internal reflection, andthe waveguide is formed at least in part from an active semiconductor; aField Effect Transistor portion (FET portion) including a gateelectrode, a source electrode, and a drain electrode; the gate electrodeis mounted to, but electrically insulated from, the activesemiconductor; the drain electrode and the source electrode are held ata substantially common voltage; wherein the gate electrode, the sourceelectrode, and the drain electrode are positioned substantially abovethe waveguide, the source electrode is located on a substantiallyopposed side of the gate electrode from the drain electrode; atwo-dimensional electron (hole) gas (2DEG) having a free carrierdistribution that is formed on a first surface of the activesemiconductor proximate the gate electrode when a voltage is appliedbetween the gate electrode and the common voltage; a voltage sourceconnected to the gate electrode for applying the voltage to the gateelectrode, wherein the gate electrode projects the region of filteringpropagation constant into the waveguide to filter light flowing throughthe waveguide; and a controller for controlling the propagation constantlevel of the region of filtering propagation constant and the lightfiltering characteristics by varying the voltage.
 42. The optical filterof claim 41 that includes an infinite-impulse-response (IIR) filtercharacterized by an output that is a linear combination of a presentinput value and past output values.
 43. The optical filter of claim 41that includes an finite-impulse-response (FIR) filter characterized byan output that is a linear combination of present and past input values.44. The optical filter of claim 41 that includes an arrayed waveguide.45. The optical filter of claim 41 that includes a frequency domainfilter region.
 46. An apparatus for filtering an input optical signal inorder to generate a filtered output optical signal, comprising: a planarelectrode positioned proximate the waveguide; means for projecting aregion of filtering propagation constant in the waveguide thatsubstantially corresponds in shape to a shape of the planar electrode byapplying a voltage to the planar electrode; and means for controlling apropagation constant level of the region of filtering propagationconstant by varying the voltage to control the filtering of lightflowing through the waveguide.
 47. A method for generating a filteredoutput optical signal by passing an input optical signal through awaveguide, comprising: providing a gate electrode proximate thewaveguide; providing a body contact electrode proximate the waveguide;applying the input optical signal to the waveguide; applying a filteringvoltage to the gate electrode that generates a region of filteringpropagation constant in the waveguide; and generating the filteredoutput optical signal in response to the input optical signal.
 48. Anapparatus for filtering an input optical signal to produce a filteredoutput signal, comprising: a planar electrode positioned proximate thewaveguide; means for applying a voltage to the planar electrode tochange the level of propagation constant in a region of filteringpropagation constant in the waveguide wherein the region of filteringpropagation constant generally corresponds in shape to a shape of theplanar electrode; and means for controlling a propagation constant levelof the region of filtering propagation constant by varying the voltageto control the filtering of light flowing through the waveguide.